题目链接
0ms

class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        //如果某个list为空就直接返回零一list
        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;
        }
    }
}