London | SDC-Nov-25 | Emiliano Uruena | Sprint 2 | Linked List Python

Sprint-2/implement_linked_list/linked_list.py

@@ -0,0 +1,59 @@
+# `push_head` should add an element to the start of the list. It should return something that can be passed to 
+# `remove` to remove that element in the future.
+# `pop_tail` should remove an element from the end of the list.
+# `remove` takes a handle from `push_head`, and removes that element from the list.
+
+class Node:
+    def __init__(self, value):
+        self.value = value      
+        self.prev = None        
+        self.next = None       
+
+
+class LinkedList:
+    def __init__(self):
+        self.head = None        
+        self.tail = None        
+
+    # adding a new value in the front of the list
+    def push_head(self, value):
+        node = Node(value)      
+
+        if self.head is None:   # if list is empty head and tail becomes this node.
+            self.head = node    
+            self.tail = node    
+        else:
+            node.next = self.head   
+            self.head.prev = node   
+            self.head = node        
+
+        return node  # returns the node so we can remove it later
+
+    # removing last element
+    def pop_tail(self):
+        if self.tail is None:   
+            raise Exception("List is empty")
+
+        value = self.tail.value  # value to return
+
+        if self.head == self.tail:  # if only one element
+            self.head = None
+            self.tail = None
+        else:
+            self.tail = self.tail.prev  # move tail back
+            self.tail.next = None       # remove old tail connection
+
+        return value
+
+    # removes a specific node 
+    def remove(self, node):
+
+        if node.prev is None:   # if removing head
+            self.head = node.next
+        else:
+            node.prev.next = node.next  # connect previous to next
+
+        if node.next is None:   # if removing tail
+            self.tail = node.prev
+        else:
+            node.next.prev = node.prev  # connect next to previous