21.合并两个有序链表.js

/*
 * @lc app=leetcode.cn id=21 lang=javascript
 *
 * [21] 合并两个有序链表
 */

// @lc code=start
/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} list1
 * @param {ListNode} list2
 * @return {ListNode}
 */
var mergeTwoLists = function (list1, list2) {
	if (list1 === null) return list2;
	if (list2 === null) return list1;
	if (list1.val < list2.val) {
		list1.next = mergeTwoLists(list1.next, list2);
		return list1;
	} else {
		list2.next = mergeTwoLists(list1, list2.next);
		return list2;
	}
};
// @lc code=end