23-merge-k-sorted-lists.js

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode[]} lists
 * @return {ListNode}
 */
const mergeKLists = (lists) => {
  const nums = [];

  for (let node of lists) {
    while (node) {
      nums.push(node.val);
      node = node.next;
    }
  }

  if (nums.length === 0) return null;

  nums.sort((a, b) => a - b);

  const newNode = new ListNode(nums[0]);

  let current = newNode;

  for (let i = 1; i < nums.length; i++) {
    current.next = new ListNode(nums[i]);
    current = current.next;
  }

  return newNode;
};