[leetcode] 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) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
assert (k >= 0);
if (head == NULL || k ==0)
return head;

ListNode *cur = head;
int cnt = 0;
while(cur!= NULL){
cur = cur->next;
cnt++;
}

if (k >= cnt)
k = k%cnt;

cur = head;
ListNode* previous = head;
if (k == 0)
return head;
while(k>0){
cur = cur->next;
k--;
}

while(cur->next){
previous = previous->next;
cur = cur ->next;
}

ListNode* tempHead = previous->next;
cur->next = head;
previous->next = NULL;

return tempHead;
}
};