https://leetcode-cn.com/problems/merge-two-sorted-lists/
将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。
示例 1:
输入:l1 = [1,2,4], l2 = [1,3,4]
输出:[1,1,2,3,4,4]
示例 2:
输入:l1 = [], l2 = []
输出:[]
示例 3:
输入:l1 = [], l2 = [0]
输出:[0]
提示:
两个链表的节点数目范围是 [0, 50]
-100 <= Node.val <= 100
l1 和 l2 均按 非递减顺序 排列
/**
* 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;
}
//2.新建一个链表作为头指针
ListNode head = new ListNode(-1);
//head是最后要返回的,所以需要一个指针去串联l1和l2
ListNode p = null;
p = head;
while(l1!=null && l2!=null){
if(l1.val < l2.val){
p.next = l1;
l1 = l1.next;
p = p.next;
}else{
p.next = l2;
l2 = l2.next;
p = p.next;
}
}
if(l1!=null){
p.next = l1;
}
if(l2!=null){
p.next = l2;
}
return head.next;
}
}