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

.

Need to pay attention to the K value. k = k % length

ListNode* rotateRight(ListNode* head, int k) {
if(!head || !head->next) return head;
ListNode* tmp = head;
int length = 0;
while(tmp) {
length++;
tmp = tmp->next;
}
k = k % length;           // k might be larger than the length of the linked list.
if(k == 0) return head;   // remember to check k value

ListNode* fast = head;
ListNode* slow = head;
while(k > 0) {
fast = fast->next;
k = k - 1;
}
while(fast && fast->next) {
slow = slow->next;
fast = fast->next;
}
ListNode* newHead = slow->next;
slow->next = NULL;
fast->next = head;
return newHead;
}