剑指 Offer 25.合并两个排序的链表点

题目描述

原题

输入两个递增排序的链表,合并这两个链表并使新链表中的节点仍然是递增排序的。

示例1:

输入:1->2->4, 1->3->4
输出:1->1->2->3->4->4

限制:

0 <= 链表长度 <= 1000

注意:本题与主站 21 题相同:https://leetcode-cn.com/problems/merge-two-sorted-lists/

题解

递归

/**
* 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) {
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;
}
}
}

迭代

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