[LintCode] Rotate List

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param head: the List
     * @param k: rotate to the right k places
     * @return: the list after rotation
     */
    public class CurrNode{
        ListNode node;
        CurrNode(ListNode node){
            this.node = node;
        }
    }
    public ListNode rotateRight(ListNode head, int k) {
        if (head == null){
            return null;
        }
        int len = getLen(head);
        k = k % len;
        ListNode preCut = head;
        ListNode curr = head;
        while (k > 0){
            curr = curr.next;
            k--;
        }
        while (curr.next != null){
            curr = curr.next;
            preCut = preCut.next;
        }
        curr.next = head;
        head = preCut.next;
        preCut.next = null; //关键，不然就不是合法链表了
        return head;
    }
    private int getLen(ListNode head){
        if (head == null){
            return 0;
        }
        int len = 0;
        while (head != null){
            head = head.next;
            len++;
        }
        return len;
    }
}