61. Rotate List

Given a list, rotate the list to the right bykplaces, wherekis non-negative.

For example:
Given1->2->3->4->5->NULLandk=2,
return4->5->1->2->3->NULL.

思路：先计算长度，取模得到移动步长。然后用双指针

    public ListNode rotateRight(ListNode head, int k) {
        if (head==null||head.next==null){
            return head;
        }
        ListNode slow = head;
        ListNode fast = head;
        //get length
        int i = 1;
        while(fast.next!=null){
            fast = fast.next;
            i++;
        }

        //move slow
        int slowstep = (i-k%i);
        if (slowstep == i){
            return head;
        }
        ListNode slowPrev = null;
        for (int j=0;j<slowstep;j++){
            slowPrev = slow;
            slow = slow.next;
        }

        //reorgnize
        fast.next = head;
        slowPrev.next = null;

        return slow;
    }

GE:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode rotateRight(ListNode head, int k){
        if(head==null ||head.next==null){
            return head;
        }

        ListNode slow = head;
        ListNode fast = head;

        int len = 0;

        while(fast!=null){
            len++;
            fast=fast.next;
        }

        fast = head;

        for(int i= 0; i<k%len; i++){
            fast = fast.next;
        }

        while(fast.next!=null){
            fast=fast.next;
            slow=slow.next;
        }

        fast.next = head;
        head=slow.next;
        slow.next = null;
        return head;
    }
}