从尾到头打印链表

题目描述
输入一个链表，按链表值从尾到头的顺序返回一个ArrayList。

package SwordOffer;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.Stack;

/** * @author jinhuajian * @data 2018年12月27日---上午11:20:21 * @blog https://me.csdn.net/qq_37119939 */

public class Solution_03 {
	public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
		ArrayList<Integer> al = new ArrayList<Integer>();
		if (listNode == null)
			return al;
		Stack<Integer> stack = new Stack<Integer>();
		ListNode head = listNode;
		while (listNode != null) {
			stack.push(listNode.val);
			listNode = listNode.next;
		}
		while (!stack.isEmpty()) {
			al.add(stack.pop());
		}
		return al;
	}

	// 递归版
	public ArrayList<Integer> printListFromTailToHead_01(ListNode listNode) {
		ArrayList<Integer> al = new ArrayList<Integer>();
		printHead(listNode, al);
		return al;
	}

	public ArrayList<Integer> printListFromTailToHead_02(ListNode listNode) {
		ArrayList<Integer> al = new ArrayList<Integer>();
		if (listNode == null)
			return al;
		printListFromTailToHead_02(listNode.next);
		return al;
	}

	public void printHead(ListNode head, ArrayList<Integer> a) {
		if (head == null)
			return;
		printHead(head.next, a);
		a.add(head.val);
	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		ListNode ln = new ListNode(1);
		ln.next = new ListNode(2);
		ln.next.next = new ListNode(3);
		ln.next.next.next = new ListNode(19);
		Solution_03 s = new Solution_03();
		ArrayList<Integer> l = s.printListFromTailToHead(ln);// 必须带泛型<Integer>
		ArrayList<Integer> l1 = s.printListFromTailToHead_01(ln);
		// 遍历ArrayList的四种方法
		for (Integer arr : l) {
			System.out.print(arr + " ");
		}
		System.out.println();
		for (int i = 0; i != l.size(); i++) {
			System.out.print(l.get(i) + " ");
		}
		System.out.println();
		Iterator<Integer> it = l.iterator();
		while (it.hasNext()) {
			System.out.print(it.next() + " ");
		}
		System.out.println();
		for (Iterator<Integer> it1 = l1.iterator(); it1.hasNext();) {
			System.out.print(it1.next() + " ");
		}
	}

}