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。

/*
 * 题目描述
 * 输入一个链表，输出该链表中倒数第k个结点。
 */

public class Main14 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ListNode head =new ListNode(0);
        ListNode[] p =new ListNode[6];
        for(int i=0;i<p.length;i++) {
            p[i] =new ListNode(i);
            if(i>0) {
                p[i-1].next = p[i];
            }else {
                head.next = p[0];
            }
        }
        ListNode result = Main14.FindKthToTail(head, 2);
        System.out.println(result.val);
    }
    
    
    public static class ListNode {
        int val;
        ListNode next = null;

        ListNode(int val) {
            this.val = val;
        }
    }
    
    public static ListNode FindKthToTail(ListNode head,int k) {
        if (head == null) {
            return null;
        }
        
        int count = 1;
        ListNode old = head;
        while(head.next != null) {
            head = head.next;
            count++;
        }
        if (k > count) {
            return null;
        }
        for(int i=0;i<count-k;i++) {
            old = old.next;
        }
        return old;
    }
}