[Leetcode]61. Rotate List

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 == nullptr || k == 0 || head->next == nullptr)
return head;
ListNode *p = head;
int len = 1;
for (; p->next != nullptr; p = p->next)
++len;
k = len - k % len;
p->next = head;
for (int i = 0; i != k; ++i)
p = p->next;
head = p->next;
p->next = nullptr;
return head;
}
};