diff --git a/linked_list/linked_list.py b/linked_list/linked_list.py index 63993214..3477e661 100644 --- a/linked_list/linked_list.py +++ b/linked_list/linked_list.py @@ -1,22 +1,26 @@ - # Defines a node in the singly linked list class Node: - def __init__(self, value, next_node = None): + def __init__(self, value, next_Node = None): self.value = value - self.next = next_node + self.next = next_Node + # Defines the singly linked list class LinkedList: def __init__(self): - self.head = None # keep the head private. Not accessible outside this class + self.head = None # keep the head private. Not accessible outside this class + self.tail = None # returns the value in the first node # returns None if the list is empty # Time Complexity: ? # Space Complexity: ? def get_first(self): - pass + if self.head is None: + return None + + return self.head.value # method to add a new node with the specific data value in the linked list @@ -24,20 +28,38 @@ def get_first(self): # Time Complexity: ? # Space Complexity: ? def add_first(self, value): - pass + if self.head is None: + self.head = self.tail = Node(value) + else: + new_Node = Node(value, self.head) + self.head.previous = new_Node + self.head = new_Node # method to find if the linked list contains a node with specified value # returns true if found, false otherwise # Time Complexity: ? # Space Complexity: ? def search(self, value): - pass + current = self.head + while current: + if current.value == value: + return True + current = current.next + return False + # method that returns the length of the singly linked list # Time Complexity: ? # Space Complexity: ? def length(self): - pass + current = self.head + count = 0 + + while current: + count += 1 + current = current.next + return count + # method that returns the value at a given index in the linked list # index count starts at 0 @@ -45,31 +67,72 @@ def length(self): # Time Complexity: ? # Space Complexity: ? def get_at_index(self, index): - pass + i = 0 + current = self.head + + while current: + if i == index: + return current.value + i += 1 + current = current.next + return None + + # method that returns the value of the last node in the linked list # returns None if the linked list is empty # Time Complexity: ? # Space Complexity: ? def get_last(self): - pass + if self.tail is None: + return None + + return self.tail.value # method that inserts a given value as a new last node in the linked list # Time Complexity: ? # Space Complexity: ? def add_last(self, value): - pass + if self.head is None: + self.head = self.tail = Node(value) + else: + new_Node = Node(value) + new_Node.previous = self.tail + self.tail.next = new_Node + self.tail = new_Node + # method to return the max value in the linked list # returns the data value and not the node def find_max(self): - pass + max_value = 0 + current = self.head + + if self.head is None: + return None + + while current is not None: + if current.value > max_value: + max_value = current.value + current = current.next + return max_value + # method to delete the first node found with specified value # Time Complexity: ? # Space Complexity: ? def delete(self, value): - pass + current = self.head + if current is None: + return None + if current.value == value: + self.head = current.next + while current.next is not None: + if current.next.value == value: + current.next = current.next.next + break + current = current.next + # method to print all the values in the linked list # Time Complexity: ? @@ -86,11 +149,25 @@ def visit(self): # method to reverse the singly linked list # note: the nodes should be moved and not just the values in the nodes - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def reverse(self): - pass - + if self.head == self.tail: + return + + current = self.head + + while current is not None: + prev = current.prev + next = current.next + current.next = prev + current.prev = next + current = next + + temp = self.head + self.head = self.tail + self.tail = temp + ## Advanced/ Exercises # returns the value at the middle element in the singly linked list # Time Complexity: ? @@ -126,3 +203,5 @@ def create_cycle(self): current = current.next current.next = self.head # make the last node link to first node + +