I just scribbled this question on Leetcode, so I remembered a classic saying: People can't even do simple questions when they are extremely angry!
The difficulty of this question marked on Leetcode is a simple question, but after thinking about it for a long time, it was painful and I didn't know what was going on. In the end, it took me more than an hour to think about it. It was basically a recursive method, combined with a linked list, so it seemed a little simple, haha!
Ideas:
answer:
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
class Solution {
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if(l1 == null){
return l2;
}
if(l2 == null){
return l1;
}
if(l1.val < l2.val){
l1.next = mergeTwoLists(l1.next,l2);
return l1;
}else{
l2.next = mergeTwoLists(l1,l2.next);
return l2;
}
}
}