Add DoublyLinkedList implementation

Author: KamilMarzynski

data_structures/3_LinkedList/3_doubly_linked_list.py

@@ -0,0 +1,66 @@
+class Node:
+    def __init__(self, data=None, next=None, prev=None):
+        self.data = data
+        self.next = next
+        self.prev = prev
+
+class LinkedList:
+    def __init__(self):
+        self.head = None
+
+
+    def print_forward(self):
+        if self.head is None:
+            print("Linked list is empty")
+            return
+        itr = self.head
+        llstr = ''
+        while itr:
+            llstr += str(itr.data)+' --> ' if itr.next else str(itr.data)
+            itr = itr.next
+        print(llstr)
+
+    def print_backward(self):
+        if self.head is None:
+            print("Linked list is empty")
+            return
+        itr = self.head
+        llstr = ''
+        while itr.next:
+            itr = itr.next
+        
+        while itr:
+            llstr += str(itr.data)+' --> ' if itr.prev else str(itr.data)
+            itr = itr.prev
+        print(llstr)
+
+    def insert_at_begining(self, data):
+        node = Node(data, self.head)
+        if self.head:
+            self.head.prev = node
+
+        self.head = node
+
+    def insert_at_end(self, data):
+        if self.head is None:
+            self.head = Node(data, None)
+            return
+
+        itr = self.head
+
+        while itr.next:
+            itr = itr.next
+
+        itr.next = Node(data, None, itr)
+
+    def insert_values(self, data_list):
+        self.head = None
+        for data in data_list:
+            self.insert_at_end(data)
+
+if __name__ == '__main__':
+    ll = LinkedList()
+    ll.insert_values(["banana","mango","grapes","orange"])
+
+    ll.print_forward()
+    ll.print_backward()