Javascript Program To Delete Middle Of Linked List

Last Updated : 03 Sep, 2024

Given a singly linked list, delete the middle of the linked list. For example, if the given linked list is 1->2->3->4->5 then the linked list should be modified to 1->2->4->5

If there are even nodes, then there would be two middle nodes, we need to delete the second middle element. For example, if given linked list is 1->2->3->4->5->6 then it should be modified to 1->2->3->5->6.

If the input linked list is NULL, then it should remain NULL.

If the input linked list has 1 node, then this node should be deleted and a new head should be returned.

Efficient solution:

Approach:

The above solution requires two traversals of the linked list. The middle node can be deleted using one traversal. The idea is to use two pointers, slow_ptr, and fast_ptr. Both pointers start from the head of list. When fast_ptr reaches the end, slow_ptr reaches middle. This idea is same as the one used in method 2 of this post. The additional thing in this post is to keep track of the previous middle so the middle node can be deleted.

Below is the implementation.

JavaScript

// Javascript program to delete the  // middle of a linked list // Link list Node  class Node {     constructor() {         this.data = 0;         this.next = null;     } }  // Deletes middle node and returns // head of the modified list function deleteMid(head) {     // Base cases     if (head == null)         return null;     if (head.next == null) {         return null;     }      // Initialize slow and fast pointers     // to reach middle of linked list     let slow_ptr = head;     let fast_ptr = head;      // Find the middle and previous of      // middle.     let prev = null;      // To store previous of slow_ptr     while (fast_ptr != null &&         fast_ptr.next != null) {         fast_ptr = fast_ptr.next.next;         prev = slow_ptr;         slow_ptr = slow_ptr.next;     }      // Delete the middle node     prev.next = slow_ptr.next;      return head; }  // A utility function to print // a given linked list function printList(ptr) {     while (ptr != null) {         console.log(ptr.data);         ptr = ptr.next;     }     console.log("NULL"); }  // Utility function to create a  // new node. function newNode(data) {     temp = new Node();     temp.data = data;     temp.next = null;     return temp; }  // Driver code  // Start with the empty list  head = newNode(1); head.next = newNode(2); head.next.next = newNode(3); head.next.next.next = newNode(4); console.log("Given Linked List"); printList(head); head = deleteMid(head); console.log("Linked List after deletion of middle"); printList(head); // This code is contributed by umadevi9616

Output

Given Linked List 1 2 3 4 NULL Linked List after deletion of middle 1 2 4 NULL

Complexity Analysis:

Time Complexity: O(n).
Only one traversal of the linked list is needed
Auxiliary Space: O(1).
As no extra space is needed.

Please refer complete article on Delete middle of linked list for more details!

Javascript Program To Delete Alternate Nodes Of A Linked List

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