LeetCode 21 Merge Two Sorted Lists

翻譯

合並兩個排好序的鏈表，並返回這個新鏈表。
新鏈表應該由這兩個鏈表的頭部拼接而成。

原文

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.

代碼

/**
 * 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(l2 == NULL) {
            return l1;
        }
        if(l1 == NULL) {
            return l2;
        }
        if(l1->val > l2->val) {
            ListNode* temp = l2;
            temp->next = mergeTwoLists(l1, l2->next);
            return temp;
        } else {
            ListNode* temp = l1;
            temp->next = mergeTwoLists(l1->next, l2);
            return temp;
        }
    }
};