[61]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 
// Related Topics 链表 双指针 
// 👍 430 👎 0

/*
* 61 旋转链表
* 2021-02-26 22:24:19
* @author oxygenbytes
*/ 
#include "leetcode.h" 
//leetcode submit region begin(Prohibit modification and deletion)
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if(!head) return nullptr;

        int n = 0;
        for(auto cur = head;cur;cur = cur->next)
            n++;

        k = k % n;
        // cout<<k<<endl;
        // return nullptr;
        auto fast = head, slow = head;

        while( k-- ) fast = fast->next;

        while(fast->next){ // stop at last node
            fast = fast->next;
            slow = slow->next;
        }

        fast->next = head;
        head = slow->next;
        slow->next = nullptr;

        return head;
    }
};
//leetcode submit region end(Prohibit modification and deletion)