16. 删除链表倒数第N个节点

<?php
Class ListNode {
    public $val = 0;
    public $next;
    public function __construct($val) {
        $this->val = $val;
    }
    public function __get($name) {
        return null;
    }
}
class Solution {
    public function removeNthFromEnd(ListNode $head, $n) {
        $dummy = new ListNode(0);
        $dummy->next = $head;
        $fastP = $dummy;
        $slowP = $dummy;
        for ($i = 0; $i <= $n; $i++) {
            $fastP = $fastP->next;
        }
        while ($fastP->next) {
            $fastP = $fastP->next;
            $slowP = $slowP->next;
        }
        $slowP->next->next = $fastP;
        return $dummy->next;
    }
}
$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();
$ret = $cls->removeNthFromEnd($head, 2);
print_r($ret);