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。

 

import java.util.ArrayList;
import java.util.Stack;
/*
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) {
        Stack<TreeNode> stack1 = new Stack<>();
        stack1.push(pRoot);
        int layer = 1;
        Stack<TreeNode> stack2 = new Stack<>();
        ArrayList<ArrayList<Integer>> list = new ArrayList<>();
        while(!stack1.empty() || !stack2.empty()) {
            if(layer%2 != 0) {
                ArrayList<Integer> temp = new ArrayList<>();
                while(!stack1.empty()) {
                    TreeNode node = stack1.pop();
                    if(node != null) {
                        temp.add(node.val);
                        stack2.push(node.left);
                        stack2.push(node.right);
                    }
                }
                if(!temp.isEmpty()) {
                    list.add(temp);
                    layer++;
                }
            }else {
                ArrayList<Integer> temp = new ArrayList<>();
                while(!stack2.empty()) {
                    TreeNode node = stack2.pop();
                    if(node != null) {
                        temp.add(node.val);
                        stack1.push(node.right);
                        stack1.push(node.left);
                    }
                }
                if(!temp.isEmpty()) {
                    list.add(temp);
                    layer++;
                }
            }
        }
        return list;
    }

}