LeetCode 21 Merge Two Sorted Lists

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本文介绍了一种通过递归方式合并两个已排序链表的方法，最终返回一个新的有序链表。该算法首先检查输入链表是否为空，然后比较两链表头结点的值，较小者作为新链表的头部，并继续递归合并剩余部分。

21. Merge Two Sorted Lists

Total Accepted: 120734 Total Submissions: 342542 Difficulty: Easy

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.

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合并两个链表，使用递归

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
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;  
        }  
    }
};