1. 程式人生 > >leetcode-21.Merge Two Sorted Lists 合併兩個有序連結串列

leetcode-21.Merge Two Sorted Lists 合併兩個有序連結串列

題目:

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.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

將兩個有序連結串列合併為一個新的有序連結串列並返回。新連結串列是通過拼接給定的兩個連結串列的所有節點組成的。 

示例:

輸入:1->2->4, 1->3->4
輸出:1->1->2->3->4->4

思路:不要生成新節點,直接返回,利用遞迴思路。

/**
 * 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;
        }
    }
};