题目

https://leetcode-cn.com/problems/merge-two-sorted-lists/

代码比较简单有2种实现方式

非递归的方式

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(0);
        ListNode p=dummy;
        while(l1!=null&&l2!=null){
            if(l1.val>l2.val){
                p.next=l2;
                l2=l2.next;
            }else{
                p.next=l1;
                l1=l1.next;
            }
            p=p.next;
        }
        if(l1!=null){
            p.next=l1;
        }
        if(l2!=null){
            p.next=l2;
        }
        return dummy.next;
        
    }
}

递归方式

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;
        }
        
        l2.next=mergeTwoLists(l1,l2.next);
        return l2;
        
    }