Al Leonard - Linked List

linked_list/linked_list.py

@@ -9,67 +9,149 @@ def __init__(self, value, next_node = None):
 # 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 # keep track of the tail
 
     # 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 == None:
+            return None
+        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
+        new_node = Node(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: ?
+    # Time Complexity: ? O(n)
+    # Space Complexity: ? O(1) because we arent creating any new data structures, nothings being changed/added
     def search(self, value):
-        pass
+        current = self.head
+        if current == None:
+            return False
+        while current:
+            if current.value == value:
+                return True
+            current = current.next
+            notTrue = True
+        if notTrue == True:
+            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
+
+        current = self.head
+        node_count = 1
+
+        while current.next != None:
+            current = current.next
+            node_count += 1
+        if node_count:
+            return node_count
+        # return current.value
 
     # 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
+        current = self.head
+        current_index = 0
+
+        while current != None:
+            if current_index == index:
+                return current.value
+            current_index += 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
+        current = self.head
+        while current.next != None:
+            current = current.next
+        return current.value
+
+    # def get_last(self): # O(1)
+    #     if self.head == None:
+    #         return None
+
+    #     return self.tail.data
 
     # 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 == None:
+            self.head = Node(value, self.head)
+        else:
+            current = self.head
+
+            while current.next != None:
+                current = current.next
+            current.next = Node(value)
 
     # method to return the max value in the linked list
     # returns the data value and not the node
     def find_max(self):
-        pass
+        current = self.head
+        max = 0
+
+        if self.head == None:
+            return None
+
+        while current != None:
+            if max < current.value:
+                max = current.value
+            current = current.next
+        return max
+
+    def find(self, value):
+        current = self.head
+
+        while current != None:
+            if current.data == value:
+                return True
+            current = current.next
+        return False
 
     # method to delete the first node found with specified value
     # Time Complexity: ?
     # Space Complexity: ?
     def delete(self, value):
-        pass
+        current = self.head
+        if current == None:
+            return None
+        elif current.value == value: 
+            self.head = current.next
+
+        while current.next != None: 
+            if current.next.value != value: 
+                current = current.next
+            else:
+                current.next = current.next.next
 
     # method to print all the values in the linked list
     # Time Complexity: ?
@@ -89,8 +171,16 @@ def visit(self):
     # Time Complexity: ?
     # Space Complexity: ?
     def reverse(self):
-        pass
-
+        current = self.head
+        previous = None
+
+        while current != None:
+            next = current.next
+            current.next = previous
+            previous = current
+            current = next
+        self.head = previous
+
     ## Advanced/ Exercises
     # returns the value at the middle element in the singly linked list
     # Time Complexity: ?
@@ -110,7 +200,7 @@ def find_nth_from_end(self, n):
     # returns true if a cycle is found, false otherwise.
     # Time Complexity: ?
     # Space Complexity: ?
-    def has_cycle(self):
+    def find_nth_from_end(self, n):
         pass
 
     # Helper method for tests