本文共 1858 字，大约阅读时间需要 6 分钟。

方法一 直接法 一个个比较

/** * 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;        }        ListNode head = new ListNode(0);        ListNode p = head;        while(l1 != null && l2 != null) {
               if(l1.val < l2.val) {
                   head.next = l1;                head = head.next;                l1 = l1.next;            }else {
                   head.next = l2;                head = head.next;                l2 = l2.next;            }        }        while(l1 != null) {
               head.next = l1;            head = head.next;            l1 = l1.next;        }         while(l2 != null) {
               head.next = l2;            head = head.next;            l2 = l2.next;        }        return p.next;    }}

方法二 递归

/** * 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) {
           return help(l1, l2);    }    public ListNode help(ListNode l1, ListNode l2) {
           if(l1 == null) {
               return l2;        }        if(l2 == null) {
               return l1;        }        if(l1.val < l2.val) {
               l1.next = help(l1.next, l2);            return l1;        }else {
               l2.next = help(l1, l2.next);            return l2;        }    }}

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