剑指offer-题23：从上往下打印二叉树

题目描述

从上往下打印出二叉树的每个节点，同层节点从左至右打印。

实验平台：牛客网

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解决思路：

java:

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;
/**
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> arrayList = new ArrayList<>();
        if (root != null) {
            Queue<TreeNode> queue = new LinkedList<TreeNode>();
            queue.offer(root);
            while (!queue.isEmpty()) {
                TreeNode tempNode = queue.poll();
                arrayList.add(tempNode.val);
                if(tempNode.left != null){
                    queue.offer(tempNode.left);
                }
                if(tempNode.right != null){
                    queue.offer(tempNode.right);
                }
            }
        }
        return arrayList;
    }
}

python:

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    # 返回从上到下每个节点值列表，例：[1,2,3]
    def PrintFromTopToBottom(self, root):
        # write code here
        list = []
        if root is not None:
            queue = []
            queue.append(root)
            while len(queue) > 0:
                tempNode = queue.pop(0)
                list.append(tempNode.val)
                if tempNode.left is not None:
                    queue.append(tempNode.left)
                if tempNode.right is not None:
                    queue.append(tempNode.right)
        return list