剑指 Offer - 16：合并两个排序链表

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题目描述

输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则

题目链接：https://www.nowcoder.com/practice/d8b6b4358f774294a89de2a6ac4d9337

public class Solution {
    public ListNode Merge(ListNode list1, ListNode list2) {
        if (list1 == null) return list2;
        if (list2 == null) return list1;
        // 递归
        ListNode head = null;
        ListNode current = null;
        while (list1 != null && list2 != null) {
            if (list1.val <= list2.val) {
                if (head == null) {
                    head = current = list1;
                } else {
                    current.next = list1;
                    current = current.next;
                }
                list1 = list1.next;
            } else {
                if (head == null) {
                    head = current = list2;
                } else {
                    current.next = list2;
                    current = current.next;
                }
                list2 = list2.next;
            }
        }
        if (list1 == null) current.next = list2;
        else current.next = list1;
        return head;
    }
}