按之字形顺序打印二叉树

题目描述

请实现一个函数按照之字形打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，其他行以此类推。

分析

贴出代码

import java.util.*;
/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        int layer = 1;

        Stack<TreeNode> s1 = new Stack<TreeNode>();
        s1.push(pRoot);

        Stack<TreeNode> s2 = new Stack<TreeNode>();

        ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();

        while (!s1.empty() || !s2.empty()){
            if (layer % 2 != 0){
                ArrayList<Integer> temp = new ArrayList<>();
                while (!s1.empty()){
                    TreeNode node = s1.pop();
                    if (node != null){
                        temp.add(node.val);
                        System.out.println(node.val + " ");
                        s2.push(node.left);
                        s2.push(node.right);
                    }
                }
                if (!temp.isEmpty()){
                    list.add(temp);
                    layer++;
                    System.out.println();
                }
            }else{
                ArrayList<Integer> temp = new ArrayList<>();
                while (!s2.empty()){
                    TreeNode node = s2.pop();
                    if (node != null){
                        temp.add(node.val);
                        System.out.println(node.val + " ");
                        s1.push(node.right);
                        s1.push(node.left);
                    }
                }
                if (!temp.isEmpty()){
                    list.add(temp);
                    layer++;
                    System.out.println();
                }
            }
        }
        return list;
    }

}