面试题5: 从尾到头打印链表

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);
}

}