LeetCode 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

 

/**
 * 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 (k == 0 || head == NULL)
            return head;

        ListNode* dummy = new ListNode(0);
        dummy->next = head;
        
        int len = 0;
        ListNode* tail = dummy;
        while (tail->next)
        {
            len++;
            tail = tail->next;
        }

        k = k % len;
        if (k)
        {
            ListNode* p = dummy;
            int cnt = len - k;
            while (cnt--)
                p = p->next;
            tail->next = dummy->next;
            dummy->next = p->next;
            p->next = NULL;
        }

        head = dummy->next;
        delete dummy;
        return head;
    }
};