2181-merge-nodes-in-between-zeros.js

/**
 * 2181. Merge Nodes in Between Zeros
 * https://leetcode.com/problems/merge-nodes-in-between-zeros/
 * Difficulty: Medium
 *
 * You are given the head of a linked list, which contains a series of integers separated
 * by 0's. The beginning and end of the linked list will have Node.val == 0.
 *
 * For every two consecutive 0's, merge all the nodes lying in between them into a single
 * node whose value is the sum of all the merged nodes. The modified list should not contain
 * any 0's.
 *
 * Return the head of the modified linked list.
 */

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var mergeNodes = function(head) {
  const result = new ListNode(0);
  let current = result;
  let sum = 0;

  head = head.next;

  while (head) {
    if (head.val === 0) {
      current.next = new ListNode(sum);
      current = current.next;
      sum = 0;
    } else {
      sum += head.val;
    }
    head = head.next;
  }

  return result.next;
};