Day 14

Doubly Linked List Implemention

Author: sandip1805

day_14_doubly_linkedlist.py

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+#Node class
+class Node:
+    # Function to initialize the node object
+    def __init__(self, data) -> None:
+        self.data = data # Assign data to instance variable
+        self.next = None # initialize next with none/null
+        self.prev = None # Initialize prev with None/null
+
+class DoublyLinkedList:
+    # Function to initialize LinkedList object
+    def __init__(self) -> None:
+        self.head = None # Initialize linked list with None/null as empty list
+        self.tail = None
+
+    # Function to add element at the start of linkedlist
+    def add(self, data):
+        # Create new Node, which will have data and next pointer as null/None          
+        temp = Node(data)
+
+        # if DoublyLinkedList itself is null/empty
+        if (self.head == None):
+            self.head = self.tail = temp
+            return
+        
+        # Set next of newly created node's next pointer to tail, as we are adding at starting of linkedlist
+        self.tail.next = temp
+        # As new node next points to head, we have to create reverse link to temp as well
+        temp.prev = self.tail
+        # Now we have to reset our head to point to the first element of linkedlist again
+        self.tail, self.tail.next = temp, None
+        
+    def insert(self, position, data):
+        node = Node(data)
+        if (position == 0):
+            node.next = self.head
+            self.head.prev = node
+            self.head = node
+        elif (position == 1):
+            temp = self.head.next
+            temp.prev = node
+            node.next = temp
+            self.head.next = node
+            node.prev = self.head
+        else:
+            temp = self.head
+            for i in range(0, position):
+                temp = temp.next
+            
+            if (temp == None):
+                self.add(data)
+            else:
+                prev = temp.prev
+                temp.prev = node
+                node.next = temp
+                node.prev = prev
+                prev.next = node
+            
+
+    
+    def print(self):
+        temp = self.head
+        while (temp):
+            print(temp.data, end = ' ')
+            temp = temp.next
+        print('\n')
+
+
+    
+    def delete(self, data):
+        # reference head in temporary variable
+        temp = self.head
+
+        # best case, if head is the element that we want to delete
+        if (temp):
+            if (temp.data == data):
+                self.head = temp.next
+                return
+        
+        # condition for other element apart from head        
+        while (temp):
+            if (temp.data == data):
+                break
+            else:
+                temp = temp.next
+            
+        # check if no data found after full iteration then return,
+        if (temp == None):
+            return
+        
+        # if data is matched, then we have to dereference matched node and remove link, and move it to
+        # next link immediate to temp next
+        prev = temp.prev
+        prev.next = temp.next        
+
+
+# Testing portion
+if __name__=='__main__':
+ 
+    llist = DoublyLinkedList()
+ 
+    llist.add(1)
+    llist.add(2)
+    llist.add(3)
+    llist.add(4)
+    llist.add(5)    
+    llist.print()
+    llist.delete(3)        
+    llist.print()
+    llist.insert(0, 6)
+    llist.print()
+    llist.insert(2, 8)
+    llist.print()
+
+