旋转链表

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.

/** * 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)        {            return head;        }                int len = 0;        ListNode *p = head;        while (p)        {            len++;            p = p->next;        }        k %= len;        if (k == 0)        {            return head;        }                p = head;        while (k)        {            p = p->next;            k--;        }        ListNode *q = head;        while (p->next)        {            p = p->next;            q = q->next;        }        ListNode *result = q->next;        p->next = head;        q->next = NULL;        return result;    }};