1、前言

2、思路

3、代码

class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1 == null || l2 == null){
            return l1 == null ? l2 : l1;
        }
        ListNode dummy = new ListNode(-1);
        ListNode p = dummy;
        while (l1 != null && l2 != null){
            if(l1.val <= l2.val){
                p.next = l1;
                l1 = l1.next;
            }else {
                p.next = l2;
                l2 = l2.next;
            }
            p = p.next;
        }
        
        p.next = l1 == null ? l2 : l1;
        return dummy.next;
    }
}