61. **!旋转链表

<?php
class ListNode {
    public $val = 0;
    public $next = null;
    function __construct($val) { $this->val = $val; }
}
class Solution {
    /**
     * @param ListNode $head
     * @param Integer $k
     * @return ListNode
     */
    public function rotateRight($head, $k) {
        $now = $head;
        $length = 1;
        while(!is_null($now->next)) {
            $now = $now->next;
            $length++;
        }
        // 头尾相连，生成旋转链表
        $now->next = $head;
        // 注意这里的边界条件是： $length - ($k % $length)
        for ($i = 0; $i < $length - ($k % $length); $i++) {
            $head = $head->next;
        }
        $res = $head->next;
        $head->next = null;
        return $res;
    }
}
$k = 1;
$head = new ListNode(1);
$head->next = new ListNode(2);
$head->next->next = new ListNode(3);
$head->next->next->next = new ListNode(4);
$head->next->next->next->next = new ListNode(5);
$cls = new Solution();
$r = $cls->rotateRight($head, $k);
print_r($r);