implement linked list

Author: PratiAmalden

Sprint-2/implement_linked_list/linked_list.py

@@ -0,0 +1,54 @@
+class Node():
+    def __init__(self, value) -> None:
+        self.value = value
+        self.next = None
+        self.previous = None
+
+class LinkedList():
+    def __init__(self) -> None:
+        self.head = None
+        self.tail = None
+
+# [1, 2 ] - 4
+    def push_head(self, value): # add element to the start of list.
+        handle = Node(value)
+        handle.next = self.head
+
+        if self.head:
+            self.head.previous = handle
+        else:
+            self.tail = handle
+        
+        self.head = handle
+        return handle
+
+# [4, 1, 2]
+    def pop_tail(self): # remove element from end of list
+        if not self.tail:
+            return None
+        
+        value = self.tail.value # 2
+        new_tail = self.tail.previous # 1
+
+        if new_tail:
+            new_tail.next = None
+        else:
+            self.head = None
+        
+        self.tail = new_tail
+        return value
+
+# [4, 1, 2] - 1
+    def remove(self, handle): # takes handle from 'push_head' + remove it
+        if handle.previous: #4
+            handle.previous.next = handle.next
+        else:
+            self.head = None
+
+        if handle.next: #2
+            handle.next.previous = handle.previous
+        else:
+            self.tail = handle.previous
+
+        handle.next = None
+        handle.previous = None