LeetCode-61. Rotate List

Given a linked list, rotate the list to the right by k places, where k is non-negative.

Example 1:

Input: 1->2->3->4->5->NULL, k = 2
Output: 4->5->1->2->3->NULL
Explanation:
rotate 1 steps to the right: 5->1->2->3->4->NULL
rotate 2 steps to the right: 4->5->1->2->3->NULL

Example 2:

Input: 0->1->2->NULL, k = 4 Output: ​​2->0->1->NULL​​ Explanation: rotate 1 steps to the right: 2->0->1->NULL rotate 2 steps to the right: 1->2->0->NULL rotate 3 steps to the right: ​​0->1->2->NULL​​​ rotate 4 steps to the right: ​​​2->0->1->NULL​​

​​题解：​​

​​先让k模一下链表长度n，避免重复操作。​​

class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        ListNode *p = head, *q = head;
        if (head == NULL || head->next == NULL) {
            return head;
        }
        int n = 1;
        while (p->next != NULL) {
            n++;
            p = p->next;
        }
        k %= n;
        if (k == 0) {
            return head;
        }
        for (int i = 1; i < n - k; i++) {
            q = q->next;
        }
        ListNode *r = q->next;
        p->next = head;
        q->next = NULL;
        return r;
    }
};