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. http://leetcode.com/onlinejudge#question_61

leetcode_rotate_list.cpp

/**
 * 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) {
        ListNode * tmp = head;
        ListNode * tail = head;
        int cnt = 0;
        while (tmp) {
            tail = tmp;
            tmp = tmp->next;
            cnt++;
        }
        if (cnt == 0)
            return NULL;
        k = k % cnt;
        if (k == 0)
            return head;
        else
            cnt = cnt - k;
        ListNode * ans = head;
        ListNode * prev = NULL;
        while (cnt--) {
            prev = ans;
            ans = ans->next;
        }
        if (prev)
            prev->next = NULL;
        if (tail)
            tail->next = head;
        return ans;
    }
};