Rotate List

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.

分析：首先遍历list得到长度，然后找到应该rotate的位置，进行rotate。注意：k有可能大于长度，因此要进行取模运算。

运行时间：12ms

/**
 * 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 || !head->next) return head;
        if(k == 0) return head;
        
        int len = 0;
        ListNode* move = head;
        while(move->next){ // find the end of the list
            len++;
            move = move->next;
        }
        ListNode* end = move;
        len++; // length of the list
        
        int count = 0;
        move->next = head;
        while(count < len - k % len){ // find the position of the rotating node
            count++;
            move = move->next;  // move is the position of the node before the rotating node
        }
        ListNode* rotate = move->next; // rotate is the position of the rotating node
        
        end->next = head;
        move->next = NULL;
        return rotate;
    }
};