#21 - Merge Two Sorted Lists

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Problem Description

Merge two sorted linked lists and return it as a sorted list.

The list should be made by splicing together the nodes of the first two lists.

Solution

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var mergeTwoLists = function(l1, l2) {
  if (!l1 || !l2) {
    return l1 || l2;
  }

  if (l1.val > l2.val) {
    [l2, l1] = [l1, l2];
  }

  l1.next = mergeTwoLists(l1.next, l2);

  return l1;
};