链表中倒数第k个节点（Java实现）

public class E22FindKthNodeFromTail {
    //链表中倒数第k个节点

    private class ListNode{
        int value;
        ListNode nextNode;
    }

    public static ListNode findKthFromTail(ListNode head, int k){
        if (head == null || k <= 0)
            return null;
        //指针ahead先行k-1步
        ListNode ahead = head;
        ListNode behind = null;
        for (int i = 0; i < k - 1; i ++){
            if (ahead == null)
                return null;
            ahead = ahead.nextNode;
        }
        //同时前进直至ahead到达末尾
        behind = head;
        while(ahead.nextNode != null){
            behind = behind.nextNode;
            ahead = ahead.nextNode;
        }

        return behind;
    }
}