Remove Node from Linked List Problem LeetCode

 You are given the head of a linked list.

Remove every node which has a node with a greater value anywhere to the right side of it.

Return the head of the modified linked list.

 

Input: head = [5,2,13,3,8]

Output: [13,8]

Explanation: The nodes that should be removed are 5, 2 and 3.

- Node 13 is to the right of node 5.

- Node 13 is to the right of node 2.

- Node 8 is to the right of node 3.

Example 2:

Input: head = [1,1,1,1]

Output: [1,1,1,1]

Explanation: Every node has value 1, so no nodes are removed.

/**

 * Definition for singly-linked list.

 * public class ListNode {

 *     int val;

 *     ListNode next;

 *     ListNode() {}

 *     ListNode(int val) { this.val = val; }

 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }

 * }

 */

class Solution {

    public ListNode removeNodes(ListNode head) {

       

 Stack<ListNode> stack = new Stack<>();

        ListNode temp = head;

        // Step 1: Traverse and process the list

        while (temp != null) {

            while (!stack.isEmpty() && stack.peek().val < temp.val) {

                stack.pop(); // Remove smaller values

            }

            stack.push(temp);

            temp = temp.next;

        }

        // Step 2: Rebuild the list from the stack

        ListNode newHead = null, prev = null;

        while (!stack.isEmpty()) {

            ListNode node = stack.pop();

            node.next = prev;

            prev = node;

        }

        return prev;

       

    }

}