腾讯//旋转链表

给定一个链表，旋转链表，将链表每个节点向右移动 k 个位置，其中 k 是非负数。

示例 1:

输入: 1->2->3->4->5->NULL, k = 2
输出: 4->5->1->2->3->NULL
解释:
向右旋转 1 步: 5->1->2->3->4->NULL
向右旋转 2 步: 4->5->1->2->3->NULL

示例 2:

输入: 0->1->2->NULL, k = 4
输出: 2->0->1->NULL
解释:
向右旋转 1 步: 2->0->1->NULL
向右旋转 2 步: 1->2->0->NULL
向右旋转 3 步: 0->1->2->NULL
向右旋转 4 步: 2->0->1->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) return NULL;
        int n = 0;
        ListNode *cur = head;
        while(cur){
            ++n;
            cur = cur->next;
        }
        k%=n;
        ListNode *fast = head, *slow = head;
        for(int i = 0; i < k; i++){
            if(fast) fast = fast->next;
        }
        if(!fast) return head;
        while(fast->next){
            fast = fast->next;
            slow = slow->next;
        }
        fast->next = head;
        fast = slow->next;
        slow->next = NULL;
        return fast;
    }
};

/**
 * 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 NULL;
        int n = 1;
        ListNode *cur = head;
        while(cur->next){
            ++n;
            cur = cur->next;
        }
        cur->next = head;
        int m = n-k%n;
        for(int i = 0; i < m; i++){
            cur = cur->next;
        }
        ListNode *newhead = cur->next;
        cur->next = NULL;
        return newhead;
    }
};