LeetCode（21）Merge Two Sorted Lists

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.

分析

数据结构与算法的链表章节的典型实例，将两个有序链表合成一个，保持其有序的性质。

AC代码

/**
 * 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;

        //合并后链表初始化为空
        ListNode *rl = NULL;

        ListNode *p = l1, *q = l2;
        if (l1->val <= l2->val)
        {
            rl = l1;
            p = l1->next;
        }
        else{
            rl = l2;
            q = l2->next;
        }
        rl->next = NULL;
        ListNode *head = rl;

        while (p && q)
        {
            if (p->val <= q->val)
            {
                rl->next = p;
                p = p->next;
            }
            else{
                rl->next = q;
                q = q->next;
            }//else
            rl = rl ->next;
        }//while

        while (p)
        {
            rl->next = p;
            p = p->next;
            rl = rl->next;
        }

        while (q)
        {
            rl->next = q;
            q = q->next;
            rl = rl->next;
        }

        return head;
    }
};

GitHub测试程序源码