剑指Offer:面试题23——从上往下打印二叉树(java实现)

问题描述：

思路：

代码：

import java.util.ArrayList;

import java.util.Queue;

import java.util.LinkedList;

public class TreeNode {

    int val = 0;

    TreeNode left = null;

    TreeNode right = null;

    public TreeNode(int val) {

        this.val = val;

    }

}

public class Solution {

    public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {

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

        if(root == null){

            return result;

        }

        Queue<TreeNode> q = new LinkedList<TreeNode>();

        q.add(root);

        while(!q.isEmpty()){

            TreeNode tmp = q.remove();

            result.add(tmp.val);

            if(tmp.left != null){

                q.add(tmp.left);

            }

            if(tmp.right != null){

                q.add(tmp.right);

            }

        }

        return result;

    }

}