LeetCode

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"For coding interview preparation, LeetCode is one of the best online resource providing a rich library of more than 300 real coding interview questions for you to practice from using one of the 7 supported languages - C, C++, Java, Python, C#, JavaScript, Ruby."

Algorithms

#	Title	Solutions	Video	Difficulty	Tag
1452	People Whose List of Favorite Companies Is Not a Subset of Another List	Solution		Medium	String, Sort
1451	Rearrange Words in a Sentence	Solution		Medium	String, Sort
1450	Number of Students Doing Homework at a Given Time	Solution		Easy	Array
1448	Count Good Nodes in Binary Tree	Solution		Medium	Tree, DFS
1447	Simplified Fractions	Solution		Medium	Math
1446	Consecutive Characters	Solution		Easy	String
1441	Build an Array With Stack Operations	Solution		Easy	Stack
1437	Check If All 1's Are at Least Length K Places Away	Solution		Medium	Array
1436	Destination City	Solution		Easy	String
1432	Max Difference You Can Get From Changing an Integer	Solution		Medium	String
1431	Kids With the Greatest Number of Candies	Solution		Easy	Array
1428	Leftmost Column with at Least a One	Solution		Medium	Array
1427	Perform String Shifts	Solution		Easy	Array, Math
1426	Counting Elements	Solution		Easy	Array
1423	Maximum Points You Can Obtain from Cards	Solution		Medium	Array, DP, Sliding Window
1422	Maximum Score After Splitting a String	Solution		Easy	String
1418	Display Table of Food Orders in a Restaurant	Solution		Medium	HashTable
1417	Reformat The String	Solution		Easy	String
1415	The k-th Lexicographical String of All Happy Strings of Length n	Solution		Medium	Backtracking
1413	Minimum Value to Get Positive Step by Step Sum	Solution		Easy	Array
1410	HTML Entity Parser	Solution		Medium	String, Stack
1409	Queries on a Permutation With Key	Solution		Medium	Array
1408	String Matching in an Array	Solution		Easy	String
1403	Minimum Subsequence in Non-Increasing Order	Solution		Easy	Greedy, Sort
1401	Circle and Rectangle Overlapping	Solution		Medium	Geometry
1400	Construct K Palindrome Strings	Solution		Medium	Greedy
1399	Count Largest Group	Solution		Easy	Array
1396	Design Underground System	Solution		Medium	Design
1395	Count Number of Teams	Solution		Medium	Array
1394	Find Lucky Integer in an Array	Solution		Easy	Array
1392	Longest Happy Prefix	Solution		Hard	String, Rolling Hash
1390	Four Divisors	Solution		Medium	Math
1389	Create Target Array in the Given Order	Solution		Easy	Array
1388	Pizza With 3n Slices	Solution		Hard	DP
1387	Sort Integers by The Power Value	Solution		Medium	Sort, Graph
1386	Cinema Seat Allocation	Solution		Medium	Array, Greedy
1385	Find the Distance Value Between Two Arrays	Solution		Easy	Array
1382	Balance a Binary Search Tree	Solution		Medium	Binary Search Tree
1381	Design a Stack With Increment Operation	Solution		Medium	Stack, Design
1380	Lucky Numbers in a Matrix	Solution		Easy	Array
1379	Find a Corresponding Node of a Binary Tree in a Clone of That Tree	Solution		Medium	Tree
1377	Frog Position After T Seconds	Solution		Hard	DFS, BFS
1376	Time Needed to Inform All Employees	Solution		Medium	DFS
1375	Bulb Switcher III	Solution		Medium	Array
1374	Generate a String With Characters That Have Odd Counts	Solution		Easy	String
1373	Maximum Sum BST in Binary Tree	Solution		Hard	DP, BST
1372	Longest ZigZag Path in a Binary Tree	Solution		Hard	DP, Tree
1371	Find the Longest Substring Containing Vowels in Even Counts	Solution		Medium	String
1370	Increasing Decreasing String	Solution		Easy	String, Sort
1367	Linked List in Binary Tree	Solution		Medium	DP, Linked List, Tree
1366	Rank Teams by Votes	Solution		Medium	Array, Sort
1365	How Many Numbers Are Smaller Than the Current Number	Solution		Easy	Array, HashTable
1362	Closest Divisors	Solution		Medium	Math
1361	Validate Binary Tree Nodes	Solution		Medium	Graph
1360	Number of Days Between Two Dates	Solution		Easy
1358	Number of Substrings Containing All Three Characters	Solution		Medium	String
1357	Apply Discount Every n Orders	Solution		Medium	Design
1356	Sort Integers by The Number of 1 Bits	Solution		Easy	Sort, Bit Manipulation
1354	Construct Target Array With Multiple Sums	Solution		Hard	Greedy
1353	Maximum Number of Events That Can Be Attended	Solution		Medium	Greedy, Sort, Segment Tree
1352	Product of the Last K Numbers	Solution		Medium	Array, Design
1351	Count Negative Numbers in a Sorted Matrix	Solution		Easy	Array, Binary Search
1349	Maximum Students Taking Exam	Solution		Hard	Dynamic Programming
1348	Tweet Counts Per Frequency	Solution		Medium	Design
1347	Minimum Number of Steps to Make Two Strings Anagram	Solution		Easy	String
1346	Check If N and Its Double Exist	Solution		Easy	Array
1345	Jump Game IV	Solution		Hard	BFS
1344	Angle Between Hands of a Clock	Solution		Medium	Math
1343	Number of Sub-arrays of Size K and Average Greater than or Equal to Threshold	Solution		Medium	Array
1342	Number of Steps to Reduce a Number to Zero	Solution		Easy	Bit Manipulation
1341	The K Weakest Rows in a Matrix	Solution		Easy
1339	Maximum Product of Splitted Binary Tree	Solution		Medium	DP, Tree
1338	Reduce Array Size to The Half	Solution		Medium
1337	Remove Palindromic Subsequences	Solution		Easy	String
1333	Filter Restaurants by Vegan-Friendly, Price and Distance	Solution		Medium
1331	Rank Transform of an Array	Solution		Easy
1329	Sort the Matrix Diagonally	Solution		Medium
1325	Delete Leaves With a Given Value	Solution		Medium	Tree
1324	Print Words Vertically	Solution		Medium	String
1323	Maximum 69 Number	Solution		Easy	Math
1317	Convert Integer to the Sum of Two No-Zero Integers	Solution		Easy
1315	Sum of Nodes with Even-Valued Grandparent	Solution		Medium	Tree, DFS
1314	Matrix Block Sum	Solution		Medium	Dynamic Programming
1313	Decompress Run-Length Encoded List	Solution		Easy	Array
1305	All Elements in Two Binary Search Trees	Solution		Medium
1304	Find N Unique Integers Sum up to Zero	Solution		Easy
1302	Deepest Leaves Sum	Solution		Medium
1300	Sum of Mutated Array Closest to Target	Solution		Medium
1299	Replace Elements with Greatest Element on Right Side	Solution		Easy
1297	Maximum Number of Occurrences of a Substring	Solution		Medium
1296	Divide Array in Sets of K Consecutive Numbers	Solution		Medium
1295	Find Numbers with Even Number of Digits	Solution	📺	Easy
1291	Sequential Digits	Solution		Medium
1290	Convert Binary Number in a Linked List to Integer	Solution		Easy
1289	Minimum Falling Path Sum II	Solution		Hard	Dynamic Programming
1287	Element Appearing More Than 25% In Sorted Array	Solution	📺	Easy
1286	Iterator for Combination	Solution		Medium	Backtracking, Design
1282	Group the People Given the Group Size They Belong To	Solution	📺	Medium
1281	Subtract the Product and Sum of Digits of an Integer	Solution		Easy
1277	Count Square Submatrices with All Ones	Solution		Medium
1275	Find Winner on a Tic Tac Toe Game	Solution		Easy	Array
1273	Delete Tree Nodes	Solution		Medium	Dynamic Programming, DFS
1271	Hexspeak	Solution		Easy
1267	Count Servers that Communicate	Solution		Medium
1266	Minimum Time Visiting All Points	Solution		Easy
1265	Print Immutable Linked List in Reverse	Solution		Medium
1261	Find Elements in a Contaminated Binary Tree	Solution		Medium	Tree, HashTable
1260	Shift 2D Grid	Solution	📺	Easy
1258	Synonymous Sentences	Solution		Medium	Backtracking
1252	Cells with Odd Values in a Matrix	Solution		Easy
1237	Find Positive Integer Solution for a Given Equation	Solution		Easy
1243	Array Transformation	Solution	📺	Easy
1232	Check If It Is a Straight Line	Solution	📺	Easy
1228	Missing Number In Arithmetic Progression	Solution		Easy
1221	Split a String in Balanced Strings	Solution		Easy	Greedy
1219	Path with Maximum Gold	Solution		Medium	Backtracking
1217	Play with Chips	Solution		Easy	Array, Math, Greedy
1214	Two Sum BSTs	Solution		Medium	Binary Search Tree
1213	Intersection of Three Sorted Arrays	Solution	📺	Easy
1209	Remove All Adjacent Duplicates in String II	Solution		Medium	Stack
1207	Unique Number of Occurrences	Solution	📺	Easy
1200	Minimum Absolute Difference	Solution	📺	Easy
1198	Find Smallest Common Element in All Rows	Solution	📺	Easy
1196	How Many Apples Can You Put into the Basket	Solution	📺	Easy
1190	Reverse Substrings Between Each Pair of Parentheses	Solution		Medium	Stack
1189	Maximum Number of Balloons	Solution	📺	Easy
1185	Day of the Week	Solution		Easy
1184	Distance Between Bus Stops	Solution	📺	Easy
1182	Shortest Distance to Target Color	Solution		Medium	Binary Search
1180	Count Substrings with Only One Distinct Letter	Solution		Easy	Math, String
1176	Diet Plan Performance	Solution		Easy	Array, Sliding Window
1175	Prime Arrangements	Solution		Easy
1165	Single-Row Keyboard	Solution		Easy
1161	Maximum Level Sum of a Binary Tree	Solution		Medium	Graph
1160	Find Words That Can Be Formed by Characters	Solution		Easy
1154	Day of the Year	Solution		Easy
1150	Check If a Number Is Majority Element in a Sorted Array	Solution	📺	Easy
1137	N-th Tribonacci Number	Solution		Easy
1134	Armstrong Number	Solution	📺	Easy
1133	Largest Unique Number	Solution	📺	Easy
1128	Number of Equivalent Domino Pairs	Solution	📺	Easy
1122	Relative Sort Array	Solution		Easy
1170	Compare Strings by Frequency of the Smallest Character	Solution		Easy
1119	Remove Vowels from a String	Solution	📺	Easy
1118	Number of Days in a Month	Solution		Easy
1108	Defanging an IP Address	Solution	📺	Easy
1104	Path In Zigzag Labelled Binary Tree	Solution		Medium	Math, Tree
1103	Distribute Candies to People	Solution		Easy	Math
1100	Find K-Length Substrings With No Repeated Characters	Solution		Medium	String, Sliding Window
1099	Two Sum Less Than K	Solution	📺	Easy
1089	Duplicate Zeros	Solution		Easy
1087	Brace Expansion	Solution		Medium	Backtracking
1086	High Five	Solution	📺	Easy
1085	Sum of Digits in the Minimum Number	Solution	📺	Easy
1079	Letter Tile Possibilities	Solution		Medium
1078	Occurrences After Bigram	Solution		Easy
1071	Greatest Common Divisor of Strings	Solution		Easy
1066	Campus Bikes II	Solution		Medium	Backtracking, DP
1065	Index Pairs of a String	Solution		Medium
1062	Longest Repeating Substring	Solution		Medium
1057	Campus Bikes	Solution		Medium
1056	Confusing Number	Solution		Easy
1055	Fixed Point	Solution		Easy
1051	Height Checker	Solution		Easy
1047	Remove All Adjacent Duplicates In String	Solution		Easy
1046	Last Stone Weight	Solution	📺	Easy
1043	Partition Array for Maximum Sum	Solution		Medium	DP
1038	Binary Search Tree to Greater Sum Tree	Solution		Medium	DFS, tree
1037	Valid Boomerang	Solution		Easy	Math
1033	Moving Stones Until Consecutive	Solution		Easy	Math
1030	Matrix Cells in Distance Order	Solution		Easy
1029	Two City Scheduling	Solution		Easy
1025	Divisor Game	Solution		Easy
1022	Sum of Root To Leaf Binary Numbers	Solution		Easy
1021	Remove Outermost Parentheses	Solution		Easy
1020	Number of Enclaves	Solution		Medium	Graph, DFS, BFS, recursion
1019	Next Greater Node In Linked List	Solution		Medium	Linked List, Stack
1018	Binary Prefix Divisible By 5	Solution		Easy
1014	Best Sightseeing Pair	Solution		Medium
1013	Partition Array Into Three Parts With Equal Sum	Solution		Easy
1011	Capacity To Ship Packages Within D Days	Solution		Medium	Binary Search
1010	Pairs of Songs With Total Durations Divisible by 60	Solution		Easy
1009	Complement of Base 10 Integer	Solution		Easy
1008	Construct Binary Search Tree from Preorder Traversal	Solution		Medium	Recursion
1005	Maximize Sum Of Array After K Negations	Solution	📺	Easy
1003	Check If Word Is Valid After Substitutions	Solution		Medium
1002	Find Common Characters	Solution		Easy
999	Available Captures for Rook	Solution		Easy
997	Find the Town Judge	Solution		Easy
994	Rotting Oranges	Solution		Easy	BFS
993	Cousins in Binary Tree	Solution		Easy	Tree, BFS
989	Add to Array-Form of Integer	Solution		Easy	Array
988	Smallest String Starting From Leaf	Solution		Medium	Tree, DFS
987	Vertical Order Traversal of a Binary Tree	Solution		Medium	Recursion
986	Interval List Intersections	Solution		Medium	Two Pointers
985	Sum of Even Numbers After Queries	Solution		Easy	Array
980	Unique Paths III	Solution		Hard	Backtracking, DFS
979	Distribute Coins in Binary Tree	Solution		Medium	Recursion
977	Squares of a Sorted Array	Solution		Easy	Array
976	Largest Perimeter Triangle	Solution		Easy	Math Array
974	Subarray Sums Divisible by K	Solution		Medium	Array
973	K Closest Points to Origin	Solution		Easy	Math Sort
970	Powerful Integers	Solution		Easy	Math
966	Vowel Spellchecker	Solution		Medium	Hash Table, String
965	Univalued Binary Tree	Solution		Easy	DFS, recursion
961	N-Repeated Element in Size 2N Array	Solution		Easy
958	Check Completeness of a Binary Tree	Solution		Medium	Tree
954	Array of Doubled Pairs	Solution	📺	Medium
953	Verifying an Alien Dictionary	Solution		Easy
951	Flip Equivalent Binary Trees	Solution		Medium	Tree, DFS, recursion
950	Reveal Cards In Increasing Order	Solution		Medium
946	Validate Stack Sequences	Solution		Medium	Stack
944	Delete Columns to Make Sorted	Solution		Easy
942	DI String Match	Solution		Easy
941	Valid Mountain Array	Solution		Easy
938	Range Sum of BST	Solution		Medium	BST, recursion, DFS
937	Reorder Log Files	Solution		Easy
935	Knight Dialer	Solution		Medium
933	Number of Recent Calls	Solution		Easy
931	Minimum Falling Path Sum	Solution		Medium	Dynamic Programming
929	Unique Email Addresses	Solution		Easy
925	Long Pressed Name	Solution		Easy
922	Sort Array By Parity II	Solution		Easy
921	Minimum Add to Make Parentheses Valid	Solution		Medium	Stack, Greedy
917	Reverse Only Letters	Solution		Easy
914	X of a Kind in a Deck of Cards	Solution		Easy
912	Sort an Array	Solution		Easy
908	Smallest Range I	Solution		Easy
900	RLE Iterator	Solution		Medium
897	Increasing Order Search Tree	Solution		Easy	DFS, recursion
896	Monotonic Array	Solution		Easy
890	Find and Replace Pattern	Solution		Medium
893	Groups of Special-Equivalent Strings	Solution	📺	Easy
888	Fair Candy Swap	Solution		Easy
885	Spiral Matrix III	Solution	📺	Medium
884	Uncommon Words from Two Sentences	Solution		Easy
883	Projection Area of 3D Shapes	Solution		Easy	Math
880	Decoded String at Index	Solution		Medium	Stack
876	Middle of the Linked List	Solution		Easy
872	Leaf-Similar Trees	Solution		Easy	DFS, recursion
868	Binary Gap	Solution		Easy
867	Transpose Matrix	Solution		Easy
860	Lemonade Change	Solution		Easy
859	Buddy Strings	Solution		Easy
856	Score of Parentheses	Solution		Medium	Stack, String
852	Peak Index in a Mountain Array	Solution		Easy
849	Maximize Distance to Closest Person	Solution		Easy
844	Backspace String Compare	Solution		Easy
841	Keys and Rooms	Solution		Easy	DFS, Graph
840	Magic Squares In Grid	Solution		Easy
836	Rectangle Overlap	Solution	📺	Easy
832	Flipping an Image	Solution		Easy
830	Positions of Large Groups	Solution		Easy
824	Goat Latin	Solution		Easy
821	Shortest Distance to a Character	Solution		Easy
819	Most Common Word	Solution		Easy	HashMap
814	Binary Tree Pruning	Solution		Medium	recursion, DFS
811	Subdomain Visit Count	Solution		Easy	HashMap
807	Max Increase to Keep City Skyline	Solution		Medium
806	Number of Lines To Write String	Solution		Easy
804	Unique Morse Code Words	Solution		Easy
800	Similar RGB Color	Solution		Easy
799	Champagne Tower	Solution		Medium
796	Rotate String	Solution		Easy
791	Custom Sort String	Solution		Medium
789	Escape The Ghosts	Solution		Medium	Math
788	Rotated Digits	Solution		Easy
784	Letter Case Permutation	Solution		Easy
783	Minimum Distance Between BST Nodes	Solution		Easy
779	K-th Symbol in Grammar	Solution		Medium
776	Split BST	Solution		Medium	Recursion
771	Jewels and Stones	Solution		Easy
769	Max Chunks To Make Sorted	Solution		Medium	Array
767	Reorganize String	Solution		Medium
766	Toeplitz Matrix	Solution		Easy
765	Couples Holding Hands	Solution		Hard
764	Largest Plus Sign	Solution		Medium	DP
763	Partition Labels	Solution		Medium
762	Prime Number of Set Bits in Binary Representation	Solution		Easy
760	Find Anagram Mappings	Solution		Easy
758	Bold Words in String	Solution		Easy
756	Pyramid Transition Matrix	Solution		Medium	Backtracking
755	Pour Water	Solution		Medium	Array
754	Reach a Number	Solution		Medium	Math
750	Number Of Corner Rectangles	Solution		Medium
748	Shortest Completing Word	Solution		Easy
747	Largest Number Greater Than Twice of Others	Solution		Easy
746	Min Cost Climbing Stairs	Solution		Easy
744	Find Smallest Letter Greater Than Target	Solution		Easy
743	Network Delay Time	Solution		Medium	Graph, Djikstra
742	Closest Leaf in a Binary Tree	Solution		Medium	Tree
740	Delete and Earn	Solution		Medium
739	Daily Temperatures	Solution		Medium
738	Monotone Increasing Digits	Solution		Medium
737	Sentence Similarity II	Solution		Medium	Union Find
735	Asteroid Collision	Solution		Medium	Stack
734	Sentence Similarity	Solution		Easy	HashTable
733	Flood Fill	Solution		Easy	BFS, DFS
729	My Calendar I	Solution		Medium
728	Self Dividing Numbers	Solution		Easy
727	Minimum Window Subsequence	Solution		Hard	DP
725	Split Linked List in Parts	Solution		Medium	LinkedList
724	Find Pivot Index	Solution		Easy	Array
723	Candy Crush	Solution		Medium	Array, Two Pointers
721	Accounts Merge	Solution		Medium	DFS, Union Find
720	Longest Word in Dictionary	Solution		Easy	Trie
719	Find K-th Smallest Pair Distance	Solution		Hard	Binary Search
718	Maximum Length of Repeated Subarray	Solution		Medium	DP
717	1-bit and 2-bit Characters	Solution		Easy
716	Max Stack	Solution		Hard	Design
714	Best Time to Buy and Sell Stock with Transaction Fee	Solution		Medium	DP
713	Subarray Product Less Than K	Solution		Medium
712	Minimum ASCII Delete Sum for Two Strings	Solution		Medium	DP
709	To Lower Case	Solution		Easy	String
706	Design HashMap	Solution		Easy	Design
705	Design HashSet	Solution		Easy	Design
704	Binary Search	Solution		Easy	Binary Search
703	Kth Largest Element in a Stream	Solution		Easy
701	Insert into a Binary Search Tree	Solution		Medium	DFS, recursion
700	Search in a Binary Search Tree	Solution		Easy	recusion, dfs
699	Falling Squares	Solution		Hard	Segment Tree
698	Partition to K Equal Sum Subsets	Solution		Medium	Backtracking
697	Degree of an Array	Solution		Easy
696	Count Binary Substrings	Solution		Easy
695	Max Area of Island	Solution		Easy	DFS
694	Number of Distinct Islands	Solution		Medium	DFS
693	Binary Number with Alternating Bits	Solution		Easy
692	Top K Frequent Words	Solution		Medium
691	Stickers to Spell Word	Solution		Hard	DP
690	Employee Importance	Solution		Easy	DFS
689	Maximum Sum of 3 Non-Overlapping Subarrays	Solution		Hard	DP
688	Knight Probability in Chessboard	Solution		Medium	DP
687	Longest Univalue Path	Solution		Easy	DFS
686	Repeated String Match	Solution		Easy
685	Redundant Connection II	Solution		Hard	Union Find
684	Redundant Connection	Solution		Medium	Union Find
683	K Empty Slots	Solution		Hard
682	Baseball Game	Solution		Easy
681	Next Closest Time	Solution		Medium
680	Valid Palindrome II	Solution		Easy	String
679	24 Game	Solution		Hard	Recursion
678	Valid Parenthesis String	Solution		Medium	Recursion, Greedy
677	Map Sum Pairs	Solution		Medium	HashMap, Trie
676	Implement Magic Dictionary	Solution		Medium
675	Cut Off Trees for Golf Event	Solution		Hard	BFS
674	Longest Continuous Increasing Subsequence	Solution		Easy
673	Number of Longest Increasing Subsequence	Solution		Medium	DP
672	Bulb Switcher II	Solution		Medium	Math
671	Second Minimum Node In a Binary Tree	Solution		Easy	Tree, DFS
670	Maximum Swap	Solution		Medium	String
669	Trim a Binary Search Tree	Solution		Easy	Tree, DFS
668	Kth Smallest Number in Multiplication Table	Solution		Hard	Binary Search
667	Beautiful Arrangement II	Solution		Medium	Array
666	Path Sum IV	Solution		Medium	Tree, DFS
665	Non-decreasing Array	Solution		Easy
664	Strange Printer	Solution		Hard	DP
663	Equal Tree Partition	Solution		Medium	Tree
662	Maximum Width of Binary Tree	Solution		Medium	BFS, DFS
661	Image Smoother	Solution		Easy	Array
660	Remove 9	Solution		Hard	Math
659	Split Array into Consecutive Subsequences	Solution		Medium	HashMap
658	Find K Closest Elements	Solution		Medium
657	Judge Route Circle	Solution		Easy
656	Coin Path	Solution		Hard	DP
655	Print Binary Tree	Solution		Medium	Recursion
654	Maximum Binary Tree	Solution		Medium	Tree
653	Two Sum IV - Input is a BST	Solution		Easy	Tree
652	Find Duplicate Subtrees	Solution		Medium	Tree
651	4 Keys Keyboard	Solution		Medium	DP
650	2 Keys Keyboard	Solution		Medium	DP
649	Dota2 Senate	Solution		Medium	Greedy
648	Replace Words	Solution		Medium	Trie
647	Palindromic Substrings	Solution		Medium	DP
646	Maximum Length of Pair Chain	Solution		Medium	DP, Greedy
645	Set Mismatch	Solution		Easy
644	Maximum Average Subarray II	Solution		Hard	Binary Search
643	Maximum Average Subarray I	Solution		Easy
642	Design Search Autocomplete System	Solution		Hard	Design
640	Solve the Equation	Solution		Medium
639	Decode Ways II	Solution		Hard	DP
638	Shopping Offers	Solution		Medium	DP, DFS
637	Average of Levels in Binary Tree	Solution		Easy
636	Exclusive Time of Functions	Solution		Medium	Stack
635	Design Log Storage System	Solution		Medium	Design
634	Find the Derangement of An Array	Solution		Medium	Math
633	Sum of Square Numbers	Solution		Easy	Binary Search
632	Smallest Range	Solution		Hard	Heap
631	Design Excel Sum Formula	Solution		Hard	Design, Topological Sort
630	Course Schedule III	Solution		Hard	Heap, Greedy
629	K Inverse Pairs Array	Solution		Hard	DP
628	Maximum Product of Three Numbers	Solution		Easy
625	Minimum Factorization	Solution		Medium
624	Maximum Distance in Arrays	Solution		Easy	Sort, Array
623	Add One Row to Tree	Solution		Medium	Tree
621	Task Scheduler	Solution		Medium	Greedy, Queue
617	Merge Two Binary Trees	Solution		Easy	Tree, Recursion
616	Add Bold Tag in String	Solution		Medium	String
611	Valid Triangle Number	Solution		Medium	Binary Search
609	Find Duplicate File in System	Solution		Medium	HashMap
606	Construct String from Binary Tree	Solution		Easy	Tree, Recursion
605	Can Place Flowers	Solution		Easy	Array
604	Design Compressed String Iterator	Solution		Easy	Design, String
600	Non-negative Integers without Consecutive Ones	Solution		Hard	Bit Manipulation, DP
599	Minimum Index Sum of Two Lists	Solution		Easy	HashMap
598	Range Addition II	Solution		Easy
594	Longest Harmonious Subsequence	Solution		Easy	Array, HashMap
593	Valid Square	Solution		Medium	Math
592	Fraction Addition and Subtraction	Solution		Medium	Math
591	Tag Validator	Solution		Hard	Stack, String
590	N-ary Tree Postorder Traversal	Solution		Easy	DFS, recursion
589	N-ary Tree Preorder Traversal	Solution		Easy	DFS, recursion
588	Design In-Memory File System	Solution		Hard	Trie, Design
587	Erect the Fence	Solution		Hard	Geometry
583	Delete Operation for Two Strings	Solution		Medium	DP
582	Kill Process	Solution		Medium	Stack
581	Shortest Unsorted Continuous Subarray	Solution		Easy	Array, Sort
576	Out of Boundary Paths	Solution		Hard	DP, DFS
575	Distribute Candies	Solution		Easy	Array
573	Squirrel Simulation	Solution		Medium	Math
572	Subtree of Another Tree	Solution		Easy	Tree
568	Maximum Vacation Days	Solution		Hard	DP
567	Permutation in String	Solution		Medium	Sliding Windows, Two Pointers
566	Reshape the Matrix	Solution		Easy
565	Array Nesting	Solution		Medium
563	Binary Tree Tilt	Solution		Easy	Tree Recursion
562	Longest Line of Consecutive One in Matrix	Solution		Medium	Matrix DP
561	Array Partition I	Solution		Easy	Array
560	Subarray Sum Equals K	Solution		Medium	Array, HashMap
559	Maximum Depth of N-ary Tree	Solution		Easy	DFS, recursion
557	Reverse Words in a String III	Solution		Easy	String
556	Next Greater Element III	Solution		Medium	String
555	Split Concatenated Strings	Solution		Medium	String
554	Brick Wall	Solution		Medium	HashMap
553	Optimal Division	Solution		Medium	String, Math
552	Student Attendance Record II	Solution		Hard	DP
551	Student Attendance Record I	Solution		Easy	String
549	Binary Tree Longest Consecutive Sequence II	Solution		Medium	Tree
548	Split Array with Equal Sum	Solution		Medium	Array
547	Friend Circles	Solution		Medium	Union Find
546	Remove Boxes	Solution		Hard	DFS, DP
545	Boundary of Binary Tree	Solution		Medium	Recursion
544	Output Contest Matches	Solution		Medium	Recursion
543	Diameter of Binary Tree	Solution		Easy	Tree/DFS/Recursion
542	01 Matrix	Solution		Medium	BFS
541	Reverse String II	Solution		Easy	String
540	Single Element in a Sorted Array	Solution		Medium
539	Minimum Time Difference	Solution		Medium	String
538	Convert BST to Greater Tree	Solution		Easy	Tree
537	Complex Number Multiplication	Solution		Medium	Math, String
536	Construct Binary Tree from String	Solution		Medium	Recursion, Stack
535	Encode and Decode TinyURL	Solution		Medium	Design
533	Lonely Pixel II	Solution		Medium	HashMap
532	K-diff Pairs in an Array	Solution		Easy	HashMap
531	Lonely Pixel I	Solution		Medium
530	Minimum Absolute Difference in BST	Solution		Easy	DFS
529	Minesweeper	Solution		Medium	BFS
527	Word Abbreviation	Solution		Hard
526	Beautiful Arrangement	Solution		Medium	Backtracking
525	Contiguous Array	Solution		Medium	HashMap
524	Longest Word in Dictionary through Deleting	Solution		Medium	Sort
523	Continuous Subarray Sum	Solution		Medium	DP
522	Longest Uncommon Subsequence II	Solution		Medium
521	Longest Uncommon Subsequence I	Solution		Easy
520	Detect Capital	Solution		Easy
517	Super Washing Machines	Solution		Hard	DP
516	Longest Palindromic Subsequence	Solution		Medium	DP
515	Find Largest Value in Each Tree Row	Solution		Medium	BFS
514	Freedom Trail	Solution		Hard	DP
513	Find Bottom Left Tree Value	Solution		Medium	BFS
509	Fibonacci Number	Solution	📺	Easy	Array
508	Most Frequent Subtree Sum	Solution		Medium	DFS, Tree
507	Perfect Number	Solution		Easy	Math
506	Relative Ranks	Solution		Easy
505	The Maze II	Solution		Medium	BFS
504	Base 7	Solution		Easy
503	Next Greater Element II	Solution		Medium	Stack
502	IPO	Solution		Hard	Heap, Greedy
501	Find Mode in Binary Tree	Solution		Easy	Binary Tree
500	Keyboard Row	Solution		Easy
499	The Maze III	Solution		Hard	BFS
496	Next Greater Element I	Solution		Easy
498	Diagonal Traverse	Solution		Medium
495	Teemo Attacking	Solution		Medium	Array
494	Target Sum	Solution		Medium
493	Reverse Pairs	Solution		Hard	Recursion
492	Construct the Rectangle	Solution		Easy	Array
491	Increasing Subsequences	Solution		Medium	Backtracking, DFS
490	The Maze	Solution		Medium	BFS
488	Zuma Game	Solution		Hard	DFS, Backtracking
487	Max Consecutive Ones II	Solution		Medium	Array
486	Predict the Winner	Solution		Medium	DP
485	Max Consecutive Ones	Solution		Easy	Array
484	Find Permutation	Solution		Medium	Array, String, Greedy
483	Smallest Good Base	Solution		Hard	Binary Search, Math
482	License Key Formatting	Solution		Medium
481	Magical String	Solution		Medium
480	Sliding Window Median	Solution		Hard	Heap
479	Largest Palindrome Product	Solution		Easy
477	Total Hamming Distance	Solution		Medium	Bit Manipulation
476	Number Complement	Solution		Easy	Bit Manipulation
475	Heaters	Solution		Easy	Array Binary Search
474	Ones and Zeroes	Solution		Medium	DP
473	Matchsticks to Square	Solution		Medium	Backtracking, DFS
472	Concatenated Words	Solution		Hard	Trie, DP, DFS
471	Encode String with Shortest Length	Solution		Hard	DP
469	Convex Polygon	Solution		Medium	Math
468	Validate IP Address	Solution		Medium	String
467	Unique Substrings in Wraparound String	Solution		Medium	DP
466	Count The Repetitions	Solution		Hard	DP
465	Optimal Account Balancing	Solution		Hard	DP
464	Can I Win	Solution		Medium	DP
463	Island Perimeter	Solution		Easy
462	Minimum Moves to Equal Array Elements II	Solution		Medium
461	Hamming Distance	Solution		Easy
460	LFU Cache	Solution		Hard	Design, LinkedHashMap, HashMap
459	Repeated Substring Pattern	Solution		Easy	String, KMP
458	Poor Pigs	Solution		Easy	Math
457	Circular Array Loop	Solution		Medium
456	132 Pattern	Solution		Medium	Stack
455	Assign Cookies	Solution		Easy
454	4Sum II	Solution		Medium	HashMap
453	Minimum Moves to Equal Array Elements	Solution		Easy
452	Minimum Number of Arrows to Burst Balloons	Solution		Medium	Array, Greedy
451	Sort Characters By Frequency	Solution		Medium	HashMap
450	Delete Node in a BST	Solution		Medium	Tree, Recursion
449	Serialize and Deserialize BST	Solution		Medium	BFS
448	Find All Numbers Disappeared in an Array	Solution		Easy	Array, HashMap
447	Number of Boomerangs	Solution		Easy	HashMap
446	Arithmetic Slices II - Subsequence	Solution		Hard	DP
445	Add Two Numbers II	Solution		Medium	Stack, LinkedList
444	Sequence Reconstruction	Solution		Medium	Topological Sort, Graph
443	String Compression	Solution		Easy
442	Find All Duplicates in an Array	Solution		Medium	Array
441	Arranging Coins	Solution		Easy
440	K-th Smallest in Lexicographical Order	Solution		Hard
439	Ternary Expression Parser	Solution		Medium	Stack
438	Find All Anagrams in a String	Solution		Easy	Sliding Window
437	Path Sum III	Solution		Easy	DFS, recursion
436	Find Right Interval	Solution		Medium	Binary Search
435	Non-overlapping Intervals	Solution		Medium	Greedy
434	Number of Segments in a String	Solution		Easy
432	All O`one Data Structure	Solution		Hard	Design
429	N-ary Tree Level Order Traversal	Solution		Easy	BFS, Tree
425	Word Squares	Solution		Hard	Trie, Backtracking, Recursion
424	Longest Repeating Character Replacement	Solution		Medium	Sliding Window
423	Reconstruct Original Digits from English	Solution		Medium	Math
422	Valid Word Square	Solution		Easy
421	Maximum XOR of Two Numbers in an Array	Solution		Medium	Bit Manipulation, Trie
420	Strong Password Checker	Solution		Hard
419	Battleships in a Board	Solution		Medium	DFS
418	Sentence Screen Fitting	Solution		Medium
417	Pacific Atlantic Water Flow	Solution		Medium	DFS
416	Partition Equal Subset Sum	Solution		Medium	DP
415	Add Strings	Solution		Easy
414	Third Maximum Number	Solution		Easy
413	Arithmetic Slices	Solution		Medium	DP
412	Fizz Buzz	Solution		Easy
411	Minimum Unique Word Abbreviation	Solution		Hard	NP-Hard, Backtracking, Trie, Recursion
410	Split Array Largest Sum	Solution		Hard	Binary Search, DP
409	Longest Palindrome	Solution		Easy
408	Valid Word Abbreviation	Solution		Easy
407	Trapping Rain Water II	Solution		Hard	Heap
406	Queue Reconstruction by Height	Solution		Medium	LinkedList, PriorityQueue
405	Convert a Number to Hexadecimal	Solution		Easy
404	Sum of Left Leaves	Solution		Easy
403	Frog Jump	Solution		Hard	DP
402	Remove K Digits	Solution		Medium	Greedy, Stack
401	Binary Watch	Solution		Easy
400	Nth Digit	Solution		Easy
399	Evaluate Division	Solution		Medium	Graph, DFS, Backtracking
398	Random Pick Index	Solution		Medium	Reservoir Sampling
397	Integer Replacement	Solution		Easy	BFS
396	Rotate Function	Solution		Easy
395	Longest Substring with At Least K Repeating Characters	Solution		Medium	Recursion
394	Decode String	Solution		Medium	Stack Depth-first-search
393	UTF-8 Validation	Solution		Medium	Bit Manipulation
392	Is Subsequence	Solution		Medium	Array, String
391	Perfect Rectangle	Solution		Hard
390	Elimination Game	Solution		Medium
389	Find the Difference	Solution			Easy
388	Longest Absolute File Path	Solution		Medium	Stack
387	First Unique Character in a String	Solution		Easy	HashMap
386	Lexicographical Numbers	Solution		Medium
385	Mini Parser	Solution		Medium	Stack
384	Shuffle an Array	Solution		Medium
383	Ransom Note	Solution		Easy	String
382	Linked List Random Node	Solution		Medium	Reservoir Sampling
381	Insert Delete GetRandom O(1) - Duplicates allowed	Solution		Hard
380	Insert Delete GetRandom O(1)	Solution		Medium	Design, HashMap
379	Design Phone Directory	Solution		Medium
378	Kth Smallest Element in a Sorted Matrix	Solution		Medium	Binary Search
377	Combination Sum IV	Solution		Medium	DP
376	Wiggle Subsequence	Solution		Medium	DP, Greedy
375	Guess Number Higher or Lower II	Solution		Medium	DP
374	Guess Number Higher or Lower	Solution		Easy	Binary Search
373	Find K Pairs with Smallest Sums	Solution		Medium	Heap
372	Super Pow	Solution		Medium	Math
371	Sum of Two Integers	Solution		Easy
370	Range Addition	Solution		Medium	Array
369	Plus One Linked List	Solution		Medium	Linked List
368	Largest Divisible Subset	Solution		Medium	DP
367	Valid Perfect Square	Solution		Medium
366	Find Leaves of Binary Tree	Solution		Medium	DFS
365	Water and Jug Problem	Solution		Medium	Math
364	Nested List Weight Sum II	Solution		Medium	DFS
363	Max Sum of Rectangle No Larger Than K	Solution		Hard	DP
362	Design Hit Counter	Solution		Medium	Design
361	Bomb Enemy	Solution		Medium
360	Sort Transformed Array	Solution		Medium	Two Pointers, Math
359	Logger Rate Limiter	Solution		Easy	HashMap
358	Rearrange String k Distance Apart	Solution		Hard	HashMap, Heap, Greedy
357	Count Numbers with Unique Digits	Solution		Medium	DP, Math
356	Line Reflection	Solution		Medium	HashSet
355	Design Twitter	Solution		Medium	Design, HashMap, Heap
354	Russian Doll Envelopes	Solution		Hard	DP, Binary Search
353	Design Snake Game	Solution		Medium
352	Data Stream as Disjoint Intervals	Solution		Hard	TreeMap
351	Android Unlock Patterns	Solution		Medium
350	Intersection of Two Arrays II	Solution	📺	Easy	HashMap, Binary Search
349	Intersection of Two Arrays	Solution	📺	Easy	Two Pointers, Binary Search
348	Design Tic-Tac-Toe	Solution		Medium	Design
347	Top K Frequent Elements	Solution		Medium	HashTable, Heap, Bucket Sort
346	Moving Average from Data Stream	Solution		Easy	Queue
345	Reverse Vowels of a String	Solution		Easy	String
344	Reverse String	Solution	📺	Easy	String
343	Integer Break	Solution		Medium	Math
342	Power of Four	Solution		Easy	Math
341	Flatten Nested List Iterator	Solution		Medium	Stack
340	Longest Substring with At Most K Distinct Characters	Solution		Hard	Sliding Window
339	Nested List Weight Sum	Solution		Easy	DFS
338	Counting Bits	Solution		Medium
337	House Robber III	Solution		Medium	DP
336	Palindrome Pairs	Solution		Hard
335	Self Crossing	Solution		Hard	Math
334	Increasing Triplet Subsequence	Solution		Medium
333	Largest BST Subtree	Solution		Medium	Tree
332	Reconstruct Itinerary	Solution		Medium	Graph, DFS
331	Verify Preorder Serialization of a Binary Tree	Solution		Medium	Stack
330	Patching Array	Solution		Hard	Greedy
329	Longest Increasing Path in a Matrix	Solution		Hard	DFS, DP
328	Odd Even Linked List	Solution		Medium	Linked List
327	Count of Range Sum	Solution		Hard	BST, Divide and Conquer
326	Power of Three	Solution		Easy	Math
325	Maximum Size Subarray Sum Equals k	Solution		Medium	HashTable
324	Wiggle Sort II	Solution		Medium	Sort
323	Number of Connected Components in an Undirected Graph	Solution		Medium
322	Coin Change	Solution		Medium	DP
321	Create Maximum Number	Solution		Hard
320	Generalized Abbreviation	Solution		Medium	Backtracking, Bit Manipulation
319	Bulb Switcher	Solution		Medium	Brainteaser
318	Maximum Product of Word Lengths	Solution		Medium
317	Shortest Distance from All Buildings	Solution		Hard
316	Remove Duplicate Letters	Solution		Hard	Stack, Recursion, Greedy
315	Count of Smaller Numbers After Self	Solution		Hard	Tree
314	Binary Tree Vertical Order Traversal	Solution		Medium	HashMap, BFS
313	Super Ugly Number	Solution		Medium
312	Burst Balloons	Solution		Hard	DP
311	Sparse Matrix Multiplication	Solution		Medium
310	Minimum Height Trees	Solution		Medium
309	Best Time to Buy and Sell Stock with Cooldown	Solution		Medium	DP
308	Range Sum Query 2D - Mutable	Solution		Hard	Tree
307	Range Sum Query - Mutable	Solution		Medium	Tree
306	Additive Number	Solution		Medium
305	Number of Islands II	Solution		Hard	Union Find
304	Range Sum Query 2D - Immutable	Solution		Medium
303	Range Sum Query - Immutable	Solution		Easy
302	Smallest Rectangle Enclosing Black Pixels	Solution		Hard	DFS, BFS
301	Remove Invalid Parentheses	Solution		Hard	BFS
300	Longest Increasing Subsequence	Solution		Medium	DP
299	Bulls and Cows	Solution		Easy
298	Binary Tree Longest Consecutive Sequence	Solution		Medium	Tree
297	Serialize and Deserialize Binary Tree	Solution		Hard	BFS
296	Best Meeting Point	Solution		Hard
295	Find Median from Data Stream	Solution		Hard	Heap
294	Flip Game II	Solution		Medium	Backtracking
293	Flip Game	Solution		Easy
292	Nim Game	Solution		Easy
291	Word Pattern II	Solution		Hard	Recursion, Backtracking
290	Word Pattern	Solution		Easy	HashMap
289	Game of Life	Solution		Medium
288	Unique Word Abbreviation	Solution		Easy
287	Find the Duplicate Number	Solution		Medium
286	Walls and Gates	Solution		Medium	BFS
285	Inorder Successor In BST	Solution		Medium	Tree
284	Peeking Iterator	Solution		Medium	Design
283	Move Zeroes	Solution	📺	Easy
282	Expression Add Operators	Solution		Hard
281	Zigzag Iterator	Solution		Medium
280	Wiggle Sort	Solution		Medium
279	Perfect Squares	Solution		Medium
278	First Bad Version	Solution	📺	Easy	Binary Search
277	Find the Celebrity	Solution		Medium
276	Paint Fence	Solution		Easy	DP
275	H-Index II	Solution		Medium	Binary Search
274	H-Index	Solution		Medium
273	Integer to English Words	Solution		Hard	Math, String
272	Closest Binary Search Tree Value II	Solution		Hard	Stack
271	Encode and Decode Strings	Solution			Medium
270	Closest Binary Search Tree Value	Solution			Easy
269	Alien Dictionary	Solution			Hard
268	Missing Number	Solution			Easy
267	Palindrome Permutation II	Solution		Medium
266	Palindrome Permutation	Solution		Easy
265	Paint House II	Solution		Hard	DP
264	Ugly Number II	Solution		Medium	DP
263	Ugly Number	Solution		Easy
261	Graph Valid Tree	Solution		Medium
260	Single Number III	Solution		Medium
259	3Sum Smaller	Solution		Medium
258	Add Digits	Solution		Easy
257	Binary Tree Paths	Solution			DFS/Recursion
256	Paint House	Solution		Medium	DP
255	Verify Preorder Sequence in Binary Search Tree	Solution		Medium	Tree
254	Factor Combinations	Solution		Medium	Backtracking
253	Meeting Rooms II	Solution		Medium	Heap
252	Meeting Rooms	Solution		Easy
251	Flatten 2D Vector	Solution		Medium
250	Count Univalue Subtrees	Solution		Medium	DFS
249	Group Shifted Strings	Solution
248	Strobogrammatic Number III	Solution		Hard	Recursion, DFS
247	Strobogrammatic Number II	Solution		Medium	Recursion
246	Strobogrammatic Number	Solution		Easy
245	Shortest Word Distance III	Solution		Medium
244	Shortest Word Distance II	Solution		Medium	HashMap
243	Shortest Word Distance	Solution		Easy
242	Valid Anagram	Solution		Easy
241	Different Ways to Add Parentheses	Solution		Medium	Divide and Conquer
240	Search a 2D Matrix II	Solution		Medium	Binary Search
239	Sliding Window Maximum	Solution		Hard	Heap
238	Product of Array Except Self	Solution		Medium	Array
237	Delete Node in a Linked List	Solution	📺	Easy	LinkedList
236	Lowest Common Ancestor of a Binary Tree	Solution		Medium	DFS
235	Lowest Common Ancestor of a Binary Search Tree	Solution		Easy	DFS
234	Palindrome Linked List	Solution	📺	Easy	Linked List
233	Number of Digit One	Solution		Hard	Math
232	Implement Queue using Stacks	Solution		Medium	Stack, Design
231	Power of Two	Solution		Easy
230	Kth Smallest Element in a BST	Solution		Medium	Tree
229	Majority Element II	Solution		Medium
228	Summary Ranges	Solution		Medium	Array
227	Basic Calculator II	Solution		Medium	String
226	Invert Binary Tree	Solution		Easy	DFS, recursion
225	Implement Stack using Queues	Solution		Easy	Stack, Queue
224	Basic Calculator	Solution		Hard
223	Rectangle Area	Solution		Easy
222	Count Complete Tree Nodes	Solution		Medium	Recursion
221	Maximal Square	Solution		Medium	Recursion
220	Contains Duplicate III	Solution	📺	Medium	TreeSet
219	Contains Duplicate II	Solution	📺	Easy	HashMap
218	The Skyline Problem	Solution		Hard	TreeMap, Design
217	Contains Duplicate	Solution	📺	Easy	HashSet
216	Combination Sum III	Solution		Medium	Backtracking
215	Kth Largest Element in an Array	Solution		Medium	Heap
214	Shortest Palindrome	Solution		Hard	KMP
213	House Robber II	Solution		Medium	DP
212	Word Search II	Solution		Hard	Trie
211	Add and Search Word - Data structure design	Solution		Medium	Trie
210	Course Schedule II	Solution		Medium
209	Minimum Size Subarray Sum	Solution		Medium
208	Implement Trie	Solution		Medium	Trie
207	Course Schedule	Solution		Medium
206	Reverse Linked List	Solution	📺	Easy	Linked List
205	Isomorphic Strings	Solution		Easy
204	Count Primes	Solution		Easy	The Sieve of Eratosthenes
203	Remove Linked List Elements	Solution		Easy
202	Happy Number	Solution		Easy
201	Bitwise AND of Numbers Range	Solution		Medium	Bit Manipulation
200	Number of Islands	Solution		Medium	Union Find, DFS
199	Binary Tree Right Side View	Solution		Medium	BFS
198	House Robber	Solution		Easy	DP
191	Number of 1 Bits	Solution		Easy	Bit Manipulation
190	Reverse Bits	Solution		Easy	Bit Manipulation
189	Rotate Array	Solution	📺	Easy
188	Best Time to Buy and Sell Stock IV	Solution		Hard	DP
187	Repeated DNA Sequences	Solution		Medium
186	Reverse Words in a String II	Solution		Medium
179	Largest Number	Solution		Medium
174	Dungeon Game	Solution		Hard	DP
173	Binary Search Tree Iterator	Solution		Medium	Stack, Design
172	Factorial Trailing Zeroes	Solution		Easy
171	Excel Sheet Column Number	Solution		Easy
170	Two Sum III - Data structure design	Solution		Easy
169	Majority Element	Solution		Easy
168	Excel Sheet Column Title	Solution		Easy
167	Two Sum II - Input array is sorted	Solution		Easy	Binary Search
166	Fraction to Recurring Decimal	Solution		Medium	HashMap
165	Compare Version Numbers	Solution		Easy
164	Maximum Gap	Solution		Hard
163	Missing Ranges	Solution
162	Find Peak Element	Solution		Binary Search
161	One Edit Distance	Solution
160	Intersection of Two Linked Lists	Solution		Easy	Linked List
159	Longest Substring with At Most Two Distinct Characters	Solution		Hard	String, Sliding Window
158	Read N Characters Given Read4 II - Call multiple times	Solution		Hard
157	Read N Characters Given Read4	Solution		Easy
156	Binary Tree Upside Down	Solution		Medium	Tree, Recursion
155	Min Stack	Solution		Easy	Stack
154	Find Minimum in Rotated Sorted Array II	Solution		Hard	Array, Binary Search
153	Find Minimum in Rotated Sorted Array	Solution		Medium	Array, Binary Search
152	Maximum Product Subarray	Solution		Medium	Array
151	Reverse Words in a String	Solution		Medium	String
150	Evaluate Reverse Polish Notation	Solution		Medium
149	Max Points on a Line	Solution		Hard
147	Insertion Sort List	Solution		Medium	Linked List
146	LRU Cache	Solution		Hard	Doubly Linked List, LinkedHashMap
145	Binary Tree Postorder Traversal	Solution	📺	Hard	Binary Tree
144	Binary Tree Preorder Traversal	Solution	📺	Medium	Binary Tree
143	Reorder List	Solution		Medium
142	Linked List Cycle II	Solution		Medium	Linked List
141	Linked List Cycle	Solution	📺	Easy	Linked List
140	Word Break II	Solution		Hard	Backtracking/DFS
139	Word Break	Solution		Medium	DP, Pruning
138	Copy List with Random Pointer	Solution		Medium	LinkedList, HashMap
137	Single Number II	Solution		Medium	Bit Manipulation
136	Single Number	Solution	📺	Easy	Bit Manipulation
135	Candy	Solution		Hard	Greedy
134	Gas Station	Solution		Medium	Greedy
133	Clone Graph	Solution		Medium	HashMap, BFS, Graph
132	Palindrome Partitioning II	Solution		Hard
131	Palindrome Partitioning	Solution		Medium
130	Surrounded Regions	Solution		Medium
129	Sum Root to Leaf Numbers	Solution		Medium	DFS
128	Longest Consecutive Sequence	Solution		Hard	Union Find
127	Word Ladder	Solution		Medium	BFS
126	Word Ladder II	Solution		Hard	BFS
125	Valid Palindrome	Solution		Easy	Two Pointers
124	Binary Tree Maximum Path Sum	Solution		Hard	Tree, DFS
123	Best Time to Buy and Sell Stock III	Solution		Hard	DP
122	Best Time to Buy and Sell Stock II	Solution		Easy	Greedy
121	Best Time to Buy and Sell Stock	Solution		Easy
120	Triangle	Solution		Medium	DP
119	Pascal's Triangle II	Solution	📺	Easy
118	Pascal's Triangle	Solution	📺	Easy
117	Populating Next Right Pointers in Each Node II	Solution		Medium	BFS
116	Populating Next Right Pointers in Each Node	Solution		Medium	BFS
115	Distinct Subsequences	Solution		Hard	DP
114	Flatten Binary Tree to Linked List	Solution		Medium	Tree
113	Path Sum II	Solution		Medium	DFS, Backtracking
112	Path Sum	Solution		Easy	DFS
111	Minimum Depth of Binary Tree	Solution		Easy	BFS, DFS
110	Balanced Binary Tree	Solution		Easy	DFS
109	Convert Sorted List to Binary Search Tree	Solution		Medium	DFS, Recursion
108	Convert Sorted Array to Binary Search Tree	Solution	📺	Easy	Tree
107	Binary Tree Level Order Traversal II	Solution		Easy	BFS
106	Construct Binary Tree from Inorder and Postorder Traversal	Solution		Medium	Recursion, Tree
105	Construct Binary Tree from Preorder and Inorder Traversal	Solution		Medium	Recursion, Tree
104	Maximum Depth of Binary Tree	Solution	📺	Easy	DFS
103	Binary Tree Zigzag Level Order Traversal	Solution		Medium	BFS,DFS
102	Binary Tree Level Order Traversal	Solution	📺	Medium	BFS
101	Symmetric Tree	Solution	📺	Easy	DFS
100	Same Tree	Solution	📺	Easy	DFS
99	Recover Binary Search Tree	Solution		Hard
98	Validate Binary Search Tree	Solution	📺	Medium	DFS/Recursion
97	Interleaving String	Solution		Hard	DP
96	Unique Binary Search Trees	Solution		Medium	Recursion, DP
95	Unique Binary Search Trees II	Solution		Medium	Recursion
94	Binary Tree Inorder Traversal	Solution	📺	Medium	Binary Tree
93	Restore IP Addresses	Solution		Medium	Backtracking
92	Reverse Linked List II	Solution		Medium
91	Decode Ways	Solution		Medium	DP
90	Subsets II	Solution		Medium	Backtracking
89	Gray Code	Solution		Medium	Bit Manipulation
88	Merge Sorted Array	Solution		Easy
87	Scramble String	Solution		Hard	Recursion
86	Partition List	Solution		Medium	Linked List
85	Maximal Rectangle	Solution		Hard	DP
84	Largest Rectangle in Histogram	Solution		Hard	Array, Stack
83	Remove Duplicates from Sorted List	Solution		Easy	Linked List
82	Remove Duplicates from Sorted List II	Solution		Medium	Linked List
81	Search in Rotated Sorted Array II	Solution		Medium	Binary Search
80	Remove Duplicates from Sorted Array II	Solution		Medium
79	Word Search	Solution		Medium	Backtracking, DFS
78	Subsets	Solution		Medium	Backtracking
77	Combinations	Solution		Medium	Backtracking
76	Minimum Window Substring	Solution		Hard	Two Pointers
75	Sort Colors	Solution		Medium	Two Pointers
74	Search a 2D Matrix	Solution		Medium	Binary Search
73	Set Matrix Zeroes	Solution		Medium
72	Edit Distance	Solution		Hard
71	Simplify Path	Solution		Medium	Stack
70	Climbing Stairs	Solution	📺	Easy	DP
69	Sqrt(x)	Solution		Easy
68	Text Justification	Solution		Hard
67	Add Binary	Solution		Easy
66	Plus One	Solution	📺	Easy
65	Valid Number	Solution		Hard
64	Minimum Path Sum	Solution		Medium	DP
63	Unique Paths II	Solution		Medium	DP
62	Unique Paths	Solution		Medium	DP
61	Rotate List	Solution		Medium	Linked List
60	Permutation Sequence	Solution		Medium	Math, Backtracking
59	Spiral Matrix II	Solution	📺	Medium
58	Length of Last Word	Solution		Easy
57	Insert Intervals	Solution		Hard	Array, Sort
56	Merge Intervals	Solution		Medium	Array, Sort
55	Jump Game	Solution		Medium	Greedy
54	Spiral Matrix	Solution	📺	Medium	Array
53	Maximum Subarray	Solution		Easy	Array
52	N-Queens II	Solution		Hard	Backtracking
51	N-Queens	Solution		Hard
50	Pow(x, n)	Solution		Medium
49	Group Anagrams	Solution		Medium	HashMap
48	Rotate Image	Solution	📺	Medium	Array
47	Permutations II	Solution		Medium	Backtracking
46	Permutations	Solution		Medium	Backtracking
45	Jump Game II	Solution		Hard	Array, Greedy
44	Wildcard Matching	Solution		Hard	Backtracking, DP, Greedy, String
43	Multiply Strings	Solution		Medium	Array, String
42	Trapping Rain Water	Solution		Hard
41	First Missing Positive	Solution		Hard	Array
40	Combination Sum II	Solution		Medium	Backtracking
39	Combination Sum	Solution		Medium	Backtracking
38	Count and Say	Solution		Easy	Recursion, LinkedList
37	Sudoku Solver	Solution		Hard
36	Valid Sudoku	Solution		Medium
35	Search Insert Position	Solution		Easy	Array
34	Search for a Range	Solution		Medium	Array, Binary Search
33	Search in Rotated Sorted Array	Solution		Medium	Binary Search
32	Longest Valid Parentheses	Solution		Hard	Stack, DP
31	Next Permutation	Solution		Medium	Array
30	Substring with Concatenation of All Words	Solution		Hard	HashMap
29	Divide Two Integers	Solution		Medium
28	Implement strStr()	Solution		Easy	String
27	Remove Element	Solution		Easy
26	Remove Duplicates from Sorted Array	Solution	📺	Easy	Array
25	Reverse Nodes in k-Group	Solution		Hard	Recursion, LinkedList
24	Swap Nodes in Pairs	Solution		Medium	Recursion, LinkedList
23	Merge k Sorted Lists	Solution	📺	Hard	Heap
22	Generate Parentheses	Solution		Medium	Backtracking
21	Merge Two Sorted Lists	Solution	📺	Easy	Recursion
20	Valid Parentheses	Solution	📺	Easy	Stack
19	Remove Nth Node From End of List	Solution	📺	Medium	Linked List
18	4 Sum	Solution		Medium	Two Pointers
17	Letter Combinations of a Phone Number	Solution		Medium	Backtracking
16	3Sum Closest	Solution		Medium	Two Pointers
15	3Sum	Solution	📺	Medium	Two Pointers, Binary Search
14	Longest Common Prefix	Solution	📺	Easy
13	Roman to Integer	Solution		Easy	Math, String
12	Integer to Roman	Solution		Medium	Math, String
11	Container With Most Water	Solution		Medium
10	Regular Expression Matching	Solution		Hard	DP
9	Palindrome Number	Java, C++		Easy
8	String to Integer (atoi)	Solution		Medium
7	Reverse Integer	Solution	📺	Easy
6	ZigZag Conversion	Solution		Easy
5	Longest Palindromic Substring	Solution		Medium
4	Median of Two Sorted Arrays	Solution		Hard	Divide and Conquer
3	Longest Substring Without Repeating Characters	Solution		Medium	HashMap, Sliding Window
2	Add Two Numbers	Solution		Medium	LinkedList
1	Two Sum	Java, C++	📺	Easy	HashMap

Database

#	Title	Solutions	Video	Difficulty	Tag
1407	Top Travellers	Solution		Easy
1384	Total Sales Amount by Year	Solution		Hard
1378	Replace Employee ID With The Unique Identifier	Solution		Easy
1369	Get the Second Most Recent Activity	Solution		Hard
1364	Number of Trusted Contacts of a Customer	Solution		Medium
1355	Activity Participants	Solution		Medium
1350	Students With Invalid Departments	Solution		Easy
1341	Movie Rating	Solution		Medium
1327	List the Products Ordered in a Period	Solution		Easy
1322	Ads Performance	Solution		Easy
1308	Running Total for Different Genders	Solution		Medium
1303	Find the Team Size	Solution		Easy
1294	Weather Type in Each Country	Solution		Easy
1285	Find the Start and End Number of Continuous Ranges	Solution		Medium
1280	Students and Examinations	Solution	📺	Easy
1270	All People Report to the Given Manager	Solution		Medium
1251	Average Selling Price	Solution		Easy
1241	Number of Comments per Post	Solution		Easy
1179	Reformat Department Table	Solution		Easy
1173	Immediate Food Delivery I	Solution		Easy
1148	Article Views I	Solution		Easy
1141	User Activity for the Past 30 Days I	Solution		Easy
1084	Sales Analysis III	Solution		Easy
1083	Sales Analysis II	Solution		Easy
1082	Sales Analysis I	Solution		Easy
1076	Project Employees II	Solution		Easy
1075	Project Employees I	Solution		Easy
1069	Product Sales Analysis II	Solution		Easy
1068	Product Sales Analysis I	Solution		Easy
1050	Actors and Directors Who Cooperated At Least Three Times	Solution		Easy
627	Swap Salary	Solution		Easy
626	Exchange Seats	Solution		Medium
620	Not Boring Movies	Solution		Easy
619	Biggest Single Number	Solution		Easy
618	Students Report By Geography	Solution		Hard	Session Variables
615	Average Salary: Departments VS Company	Solution		Hard
614	Second Degree Follower	Solution		Medium	Inner Join
613	Shortest Distance in a Line	Solution		Easy
612	Shortest Distance in a Plane	Solution		Medium
610	Triangle Judgement	Solution		Easy
608	Tree Node	Solution		Medium	Union
607	Sales Person	Solution		Easy
603	Consecutive Available Seats	Solution		Easy
602	Friend Requests II: Who Has the Most Friends	Solution		Medium
601	Human Traffic of Stadium	Solution		Hard
597	Friend Requests I: Overall Acceptance Rate	Solution		Easy
596	Classes More Than 5 Students	Solution		Easy
595	Big Countries	Solution		Easy
586	Customer Placing the Largest Number of Orders	Solution		Easy
585	Investments in 2016	Solution		Medium
584	Find Customer Referee	Solution		Easy
580	Count Student Number in Departments	Solution		Medium	Left Join
578	Get Highest Answer Rate Question	Solution		Medium
577	Employee Bonus	Solution		Easy
574	Winning Candidate	Solution		Medium
571	Find Median Given Frequency of Numbers	Solution		Hard
570	Managers with at Least 5 Direct Reports	Solution		Medium
569	Median Employee Salary	Solution		Hard
534	Game Play Analysis III	Solution		Easy
512	Game Play Analysis II	Solution		Easy
511	Game Play Analysis I	Solution		Easy
262	Trips and Users	Solution		Hard	Inner Join
197	Rising Temperature	Solution		Easy
196	Delete Duplicate Emails	Solution		Easy
185	Department Top Three Salaries	Solution		Hard
184	Department Highest Salary	Solution		Medium
183	Customers Who Never Order	Solution		Easy
182	Duplicate Emails	Solution		Easy
181	Employees Earning More Than Their Managers	Solution		Easy
180	Consecutive Numbers	Solution		Medium
178	Rank Scores	Solution		Medium
177	Nth Highest Salary	Solution		Medium
176	Second Highest Salary	Solution		Easy
175	Combine Two Tables	Solution		Easy

Shell

#	Title	Solutions	Video	Difficulty	Tag
195	Tenth Line	Solution		Easy
194	Transpose File	Solution		Medium
193	Valid Phone Numbers	Solution		Easy
192	Word Frequency	Solution		Medium

Contributing

Your ideas/fixes/algorithms are more than welcome!

1. Fork this repo
2. Clone your forked repo (git clone https://github.com/YOUR_GITHUB_USERNAME/Leetcode.git) onto your local machine
3. cd into your cloned directory, create your feature branch (git checkout -b my-awesome-fix)
4. git add your desired changes to this repo
5. Commit your changes (git commit -m 'Added some awesome features/fixes')
6. Push to the branch (git push origin my-awesome-feature)
7. Open your forked repo on Github website, create a new Pull Request to this repo!

Best way to open this project

1. Install Intellij on your machine, either CE or UE.
2. git clone this repo to your local disk
3. import this project as a new project (does need to be imported as a gradle project)
4. If you run into "Could not determine Java version using executable ..." error, use local gradle distribution: "/usr/local/Cellar/gradle/4.8.1/libexec/" instead of the default one. More details, see Stackoverflow.