leetcode 061 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.

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/**
 * 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) {
        int len = 0;
		ListNode *l = head;
		ListNode *ret = NULL;
		if(head == NULL) return ret;

		while(l != NULL) {
			len++;
			l = l->next;
		}

		k = k%len;
		
		if(k == 0) return head;

		int kk = len-k;
		kk = kk-1;

		l = head;

		while(kk--) {
			l = l->next;
		}

		ListNode *next = l->next;
		l->next = NULL;

		ret = next;

		for(; next->next!=NULL; next=next->next);

		next->next = head;

		return ret;
    }
};