LeetCode 61. Rotate List

/**
 * 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) return NULL;
        ListNode *cur = head;
        int n = 0;
        while(cur) {
            cur = cur->next;
            ++n;
        }
                
        ListNode *slow = head;
        ListNode *fast = head;
        
        k %= n;
        for (int i = 0; i < k; ++i) {
            if (fast) fast = fast->next;
        }

        if (!fast) return head;
        
        while(fast->next) {
            fast = fast->next;
            slow = slow->next;
        }
        fast->next = head;
        fast = slow->next;
        slow->next = NULL;
        return fast;
    }
};