面试题5: 从尾到头打印链表

一. 题目

输入一个链表的头结点,从尾到头反过来打印出每个节点的值.

代码请到我的代码库中下载 Point2Offer

二. 代码

package com;

import java.util.Stack;

/**
 * 剑指offer: 从尾到头输出列表
 * 两种考虑:1.不改变链表结构(栈,递归);2.改变链表结构(遍历/递归,见链表反转,这里不考虑)
 * 测试用例三种(链表有多个节点,一个节点核链表为空)
 * @author dingding
 * Date:2017-6-14 15:06
 * Declaration: All Rights Reserved!
 */

public class PrintReversedList {

    public static void main(String[] args) {
        test3();
        test2();
        test1();
    }

    //方法1: 使用栈
    private static void printByStack(ListNode pHead){
        Stack<Integer> list = new Stack<Integer>();
        if (pHead==null) {
            System.out.println("空链表");
        }else{
            while (pHead!=null){
                list.push((Integer)pHead.getValue());
                pHead = pHead.getNext();
            }

            while (!list.isEmpty()){
                Integer a = list.pop();
                System.out.print(a+" ");
            }
            System.out.println();
        }
    }

    //方法2:使用递归
    private static void printByRecursive(ListNode pHead){
        if (pHead!=null) {
            if (pHead.getNext()!=null){
                printByRecursive(pHead.getNext());
            }
            System.out.print(pHead.getValue()+" ");   //若放在46行,结果会出错
        }else{
            System.out.println("空链表!");
        }
    }

    //打印链表
    private static void printList(ListNode first) {
        if (first==null) {
            System.out.println("空链表!");
        }else{
            while (first!=null){
                System.out.print(first.getValue()+" ");
                first = first.getNext();
            }
            System.out.println();
        }
    }

    //===========测试用例===============
    private static void test(ListNode first){
        System.out.println("初始链表:");
        printList(first);
        System.out.println("使用栈从尾到头打印链表:");
        printByStack(first);
        System.out.println("递归从尾到头打印链表:");
        printByRecursive(first);
        System.out.println();
    }

    //链表有多个节点
    private static void test3() {
        ListNode first = new ListNode(1);
        ListNode second = new ListNode(2);
        ListNode third = new ListNode(3);
        ListNode fourth = new ListNode(4);

        first.setNext(second);
        second.setNext(third);
        third.setNext(fourth);

        test(first);
        System.out.println("=============================");
    }

    //链表只有一个节点
    private static void test2() {
        ListNode first = new ListNode(1);
        test(first);
        System.out.println("=============================");
    }

    //链表为空
    private static void test1() {
        test(null);
    }

}

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有不妥当之处,麻烦告知:D