链表中倒数第k个结点

题目描述

输入一个链表，输出该链表中倒数第k个结点。

function FindKthToTail($head, $k)
{
    if ($k == 0 || $head == NULL) {
    	return NULL;
    }
    $pre = $head;
    $last = $head;
   	while ($k>1) {
   		$k--;
   		if ($last -> next == NULL) {
   			return NULL;
   		} else {
   			$last = $last -> next;
   		}
   	}
   	while ($last -> next != NULL) {
   		$pre = $pre -> next;
   		$last = $last -> next;
   	}
   	return $pre;
}