Linked List CS Fun Project

linked_list/linked_list.py

@@ -13,63 +13,144 @@ def __init__(self):
 
     # returns the value in the first node
     # returns None if the list is empty
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: 0(1)
+    # Space Complexity: 0(n)
     def get_first(self):
-        pass
+        if self.head == None:
+            return None
+#The other scenario would mean there is a value in the first node or the 1st node exists. 
+        else:
+            return self.head.value
 
+
 
     # method to add a new node with the specific data value in the linked list
     # insert the new node at the beginning of the linked list
     # Time Complexity: ?
     # Space Complexity: ?
     def add_first(self, value):
-        pass
+        if self.head == None:
+            new_node = Node(value=value, next_node=None)
+            self.head= new_node
+        else:
+            new_node = Node(value=value, next_node=self.head)
+            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
+        if self.head == None:
+            return False
+        else:
+            current = self.head
+            while current != None:
+                if current.value == value:
+                    return True
+                else:
+                    current = current.next
+            return False
+
 
     # method that returns the length of the singly linked list
     # Time Complexity: ?
     # Space Complexity: ?
     def length(self):
-        pass
+        if self.head == None:
+            return 0
+        else:
+            counter = 0
+            current = self.head
+            while current != None:
+                counter += 1
+                current = current.next
+            return counter 
+
 
     # method that returns the value at a given index in the linked list
     # index count starts at 0
     # returns None if there are fewer nodes in the linked list than the index value
     # Time Complexity: ?
     # Space Complexity: ?
     def get_at_index(self, index):
-        pass
+        if self.head == None:
+            return None
+        else:
+            counter = 0 
+            current = self.head
+            while current != None:
+                if counter == index:
+                    return current.value
+                else:
+                    counter += 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.head == None:
+            return None
+        else:
+            current = self.head
+            while current != None:
+                if current.next == None:
+                    return current.value
+                else:
+                    current = current.next
 
     # 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
+        new_node = Node(value, next_node=None)
+        if self.head == None:
+            self.head = new_node
+        else:
+            current = self.head
+            while current != None:
+                if current.next == None:
+                    new_node = Node(value, next_node=None)
+                    current.next = new_node
+                    current = current.next
+                    return 
+                else:
+                    current = current.next
 
     # method to return the max value in the linked list
     # returns the data value and not the node
     def find_max(self):
-        pass
+        if self.head == None:
+            return None
+        else:
+            final_max = self.head.value
+            current = self.head.next
+            while current != None:
+                if current.value > final_max:
+                    final_max = current.value
+                current = current.next
+            return final_max
 
     # method to delete the first node found with specified value
     # Time Complexity: ?
     # Space Complexity: ?
     def delete(self, value):
-        pass
+        if self.head == None:
+            return None
+        elif self.head.value == value:
+            self.head = self.head.next
+        else:
+            current = self.head
+            while current.next != None:
+                if current.next.value == value:
+                    current.next = current.next.next
+                    return 
+                else:
+                    current = current.next
 
     # method to print all the values in the linked list
     # Time Complexity: ?
@@ -89,29 +170,87 @@ def visit(self):
     # Time Complexity: ?
     # Space Complexity: ?
     def reverse(self):
-        pass
+        if self.head == None:
+            return 
+        elif self.head.next == None:
+            return
+        else:
+            current = self.head
+            reversed_link = None
+            while current.next != None:
+                if not reversed_link:
+                    next_node = current.next
+                    current.next = None
+                    reversed_link = current
+                    current = next_node
+                else:
+                    next_node = current.next
+                    current.next = reversed_link
+                    reversed_link = current
+                    current = next_node
+            current.next = reversed_link
+            reversed_link = current
+            self.head = reversed_link
+            return self
 
     ## Advanced/ Exercises
     # returns the value at the middle element in the singly linked list
     # Time Complexity: ?
     # Space Complexity: ?
     def find_middle_value(self):
-        pass
+        if self.head == None:
+            return None
+        elif self.head.next == None:
+            return self.head.value
+        else:
+            one_step_current = self.head
+            two_step_current = self.head
+            while two_step_current != None and two_step_current.next != None:
+                one_step_current = one_step_current.next
+                two_step_current = two_step_current.next.next
+            return one_step_current.value
 
     # find the nth node from the end and return its value
     # assume indexing starts at 0 while counting to n
     # Time Complexity: ?
     # Space Complexity: ?
     def find_nth_from_end(self, n):
-        pass
+        if self.head == None:
+            return None
+        else:
+            one_step_current = self.head
+            n_step_current = self.head
+            counter = 0
+            while n_step_current.next != None:
+                if counter < n:
+                    n_step_current = n_step_current.next
+                    counter += 1
+                else:
+                    n_step_current = n_step_current.next
+                    one_step_current = one_step_current.next
+            if counter < n:
+                return None
+            else:
+                return one_step_current.value
 
     # checks if the linked list has a cycle. A cycle exists if any node in the
     # linked list links to a node already visited.
     # returns true if a cycle is found, false otherwise.
     # Time Complexity: ?
     # Space Complexity: ?
     def has_cycle(self):
-        pass
+        if self.head == None:
+            return False
+        else:
+            node_set = set()
+            current = self.head
+            while current != None:
+                if current not in node_set:
+                    node_set.add(current)
+                    current = current.next
+                else:
+                    return True
+            return False
 
     # Helper method for tests
     # Creates a cycle in the linked list for testing purposes
@@ -125,4 +264,4 @@ def create_cycle(self):
         while current.next != None:
             current = current.next
 
-        current.next = self.head # make the last node link to first node
+        current.next = self.head # make the last node link to first node