[LeetCode]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.

思考：先首尾连成环，head前进(len-k%len)步，拆环。

/**
 * 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==NULL||k==0) return head;
        ListNode *p=head;
        int len=1;
        while(p->next)
        {
            len++;
            p=p->next;
        }
        p->next=head;
        k%=len;
        int step=len-k;
        while(step--)
        {
            p=p->next;
        }
        head=p->next;
        p->next=NULL;
        return head;
    }
};