链表中倒数第k个结点

输入一个链表，输出该链表中倒数第k个结点。

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/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode FindKthToTail(ListNode head,int k) {
        if(head == null || k <= 0)
            return null;

        ListNode first = head;
        ListNode second = head;
        for(int i = 0; i < k -1; ++i)
            {
            if(first.next != null)
                first = first.next;
            else
                return null;
        }
        while(first.next != null)
            {
            first = first.next;
            second = second.next;
        }
        return second;
    }
}