Rotate_list

/*Problem: 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) {
    if (head==NULL||k==0) return head;
    ListNode *newHead=head, *p1=head;
    while (k>0){
        newHead=newHead->next;
        if (newHead==NULL) newHead=head;
        k--;
    }
    //we next move newHead to the beginning of the new list and p1 to the tail of the new list.
    while(newHead->next){
        newHead=newHead->next;
        p1=p1->next;
    }
    //now newHead points to the beginning of the new list and p1 points to the tail of the new list.
    newHead->next=head;
    head=p1->next;
    p1->next=NULL;
    return head;
}
};

REMARK:
1. This seems to be an easy one. But it can be tricky.
I first did not get the meaning of the problem.
IDEA: create 2 pointers that track the tail and the beginning of the new list repectively. The method is hard to describe but can be easily seen via code.
2. Efficiency: max(k,n) where n is the length of the list.