[LeetCode61]Rotate List

题目：

Given a list, rotate the list to the right by k places, where k is non-negative.

For example:
Given 1->2->3->4->5->NULL and k = 2,
return 4->5->1->2->3->NULL.

分类：LinkedList   TwoPointers

代码：关键构造一个环再从相应位置断开

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if(!head)
            return head;
        int length = 1;
        ListNode *newHead, *tail;
        newHead = tail = head;
        //得到结点数
        while(tail->next)
        {
            tail = tail->next;
            length++;
        }
        //构造一个换
        tail->next = head;
        
        if(k %= length)
        {
            for(int i = 0; i < length - k; ++i)
                tail = tail->next;
        }
        newHead = tail->next;
        tail->next = NULL;
        return newHead;
    }
};