# 蜗牛慢慢爬 LeetCode 21. Merge Two Sorted Lists [Difficulty: Easy]

题目

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

翻译

合并两个有序的链表

Hints

Related Topics: LinkedList

参考 归并排序-维基百科，可以递归也可以迭代，基本的链表操作

代码

Java

/**
 * 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;
        }
    }
}

Python

//recursively
class Solution(object):
    def mergeTwoLists(self, l1, l2):
        if l1==None:    return l2;
        if l2==None:    return l1;
        
        if l1.val<l2.val:
            l1.next = self.mergeTwoLists(l1.next,l2)
            return l1
        else:
            l2.next = self.mergeTwoLists(l1,l2.next)
            return l2

//iteratively
class Solution(object):
    def mergeTwoLists(self, l1, l2):
        dummy = curr = ListNode(0)
        
        while l1 and l2:
            if l1.val<l2.val:
                curr.next = l1
                l1 = l1.next
            else:
                curr.next = l2
                l2 = l2.next
            curr = curr.next
        curr.next = l1 or l2
        return dummy.next