61. Rotate List（js）

61. Rotate List

Given a linked list, rotate the list to the right by k places, where k is non-negative.

Example 1:

Input: 1->2->3->4->5->NULL, k = 2
Output: 4->5->1->2->3->NULL
Explanation:
rotate 1 steps to the right: 5->1->2->3->4->NULL
rotate 2 steps to the right: 4->5->1->2->3->NULL

Example 2:

Input: 0->1->2->NULL, k = 4
Output: 2->0->1->NULL
Explanation:
rotate 1 steps to the right: 2->0->1->NULL
rotate 2 steps to the right: 1->2->0->NULL
rotate 3 steps to the right: 0->1->2->NULL
rotate 4 steps to the right: 2->0->1->NULL
题意：旋转k次链表，每旋转一次即把链表尾部节点取下放到链表头部
代码如下：

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} k
 * @return {ListNode}
 */
var rotateRight = function(head, k) {
    if(!head) return null;
    let n=0;
    let cur=head;
    while(cur){
        n++;
        cur=cur.next;
    }
    k%=n;
    let fast=head,slow=head;
    for(let 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;
};