[LeetCode]25.Reverse Nodes in k-Group

【题目】

Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.

If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it is.

You may not alter the values in the nodes, only nodes itself may be changed.

Only constant memory is allowed.

For example,
Given this linked list: 1->2->3->4->5

For k = 2, you should return: 2->1->4->3->5

For k = 3, you should return: 3->2->1->4->5

【题意】

给定一个链表，一次反转链表前k个节点，并返回它的修改链表。

如果节点的数量是不k的倍数则最终留出节点应该保持原样，每K个一反转，不到k个不用反转。

【分析】

无

【代码】

/*********************************
*   日期：2014-01-31
*   作者：SJF0115
*   题号: Reverse Nodes in k-Group
*   来源：http://oj.leetcode.com/problems/reverse-nodes-in-k-group/
*   结果：AC
*   来源：LeetCode
*   总结：
**********************************/
#include <iostream>
#include <stdio.h>
#include <algorithm>
using namespace std;

struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};

class Solution {
public:
    ListNode *reverseKGroup(ListNode *head, int k) {
        if (head == NULL || k < 2){
            return head;
        }

        ListNode *dummy = (ListNode*)malloc(sizeof(ListNode));
        dummy->next = head;

        ListNode *pre = dummy,*cur = NULL,*tail = NULL;
        //统计节点个数
        int count = 0;
        while(pre->next != NULL){
            pre = pre->next;
            count++;
        }
        //反转次数
        int rCount = count / k;
        int index = 0;
        //反转元素的前一个
        pre = dummy;
        //反转元素第一个即翻转后的尾元素
        tail = dummy->next;
        //共进行rCount次反转
        while(index < rCount){
            int i = k - 1;
            //反转
            while(i > 0){
                //删除cur元素
                cur = tail->next;
                tail->next = cur->next;
                //插入cur元素
                cur->next = pre->next;
                pre->next = cur;
                i--;
            }
            pre = tail;
            tail = pre->next;
            index++;
        }
        return dummy->next;
    }
};
int main() {
    Solution solution;
    int A[] = {1,2,3,4,5};
    ListNode *head = (ListNode*)malloc(sizeof(ListNode));
    head->next = NULL;
    ListNode *node;
    ListNode *pre = head;
    for(int i = 0;i < 5;i++){
        node = (ListNode*)malloc(sizeof(ListNode));
        node->val = A[i];
        node->next = NULL;
        pre->next = node;
        pre = node;
    }
    head = solution.reverseKGroup(head->next,5);
    while(head != NULL){
        printf("%d ",head->val);
        head = head->next;
    }
    return 0;
}

【代码】