按之字形打印二叉树

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> []level = new Stack[2];
        level[0] = new Stack<TreeNode>();
        level[1] = new Stack<TreeNode>();
        ArrayList<ArrayList<Integer>> ans = new ArrayList<>();
        if (pRoot == null) return ans;
        level[0].push(pRoot);
        int now = 0;
        ArrayList<Integer> l = new ArrayList<>();
        int num = 0;
        while (!level[0].empty() || !level[1].empty()) {
            TreeNode temp = level[now].pop();
            l.add(temp.val);
            int next = (now + 1) % 2;
            if (num % 2 == 0) {
                if (temp.left != null) {
                    level[next].push(temp.left);
                }
                if (temp.right != null){
                    level[next].push(temp.right);
                }
                
            } else {
                if (temp.right != null){
                    level[next].push(temp.right);
                }
                if (temp.left != null) {
                    level[next].push(temp.left);
                }
                
            }
            if (level[now].empty()) {
                now = (now + 1) % 2;
                num++;
                ans.add(new ArrayList<Integer>(l));
                l = new ArrayList<>();
            }
            
            
        }
        return ans;
    }

}