[LeetCode] 21. Merge Two Sorted Lists

题目链接：传送门

Description

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

Solution

题意：

合并两个有序序列

思路：

直接合并，太久没接触指针已是生疏，琢磨了老半天...

/**
 * 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) {
        ListNode *head = NULL, **p = &head;
        while (l1 != NULL || l2 != NULL) {
            if (l2 == NULL || (l1 != NULL && l1->val < l2->val)) {
                *p = l1;
                l1 = l1->next;
            } else {
                *p = l2;
                l2 = l2->next;
            }
            p = &((*p)->next);
        }
        return head;
    }
};

补充：

在 Discuss 中有挺多写法可以借鉴的，也有递归的写法

21. Merge Two Sorted Lists - Discuss