【简单】剑指 Offer 25. 合并两个排序的链表

题目描述

输入两个递增排序的链表，合并这两个链表并使新链表中的节点仍然是递增排序的。

示例1：

输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4
限制：

0 <= 链表长度 <= 1000

注意：本题与主站 21 题相同：https://leetcode-cn.com/problems/merge-two-sorted-lists/

通过次数61,236提交次数83,165

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/he-bing-liang-ge-pai-xu-de-lian-biao-lcof
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题解

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var mergeTwoLists = function(l1, l2) {
    if (l1 === null) return l2;
    if (l2 === null) return l1;
    let root = null;
    if (l1.val < l2.val) {
        root = new ListNode(l1.val);
        l1 = l1.next;
    } else {
        root = new ListNode(l2.val);
        l2 = l2.next;
    }
    let now = root;
    while (l1 || l2) {
        if (l1 === null) {
            now.next = l2;
            break;
        }
        if (l2 === null) {
            now.next = l1;
            break;
        }
        if (now.val === l1.val || l1.val <= l2.val) {
            now.next = new ListNode(l1.val);
            now = now.next;
            l1 = l1.next;
        } else if (now.val === l2.val || l2.val <= l1.val) {
            now.next = new ListNode(l2.val);
            now = now.next;
            l2 = l2.next;
        }
    }
    return root;
};