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

// test20.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<iostream>
#include<vector>
#include<string>
#include<queue>
#include<stack>

using namespace std;



struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
	val(x), left(NULL), right(NULL) {
	}
};
class Solution {
public:
	vector<int> PrintFromTopToBottom(TreeNode *root) {
		vector<int> vec;
		queue<TreeNode* > qu;
		if (root == NULL)return vec;
		qu.push(root);
		while (!qu.empty())
		{
			//cout << qu.front()->val << "  ";
			vec.push_back(qu.front()->val);
			if (qu.front()->left != NULL) qu.push(qu.front()->left);
			if (qu.front()->right != NULL) qu.push(qu.front()->right);
			qu.pop();
		}
		return vec;
	}


	void preCreate(TreeNode* &T)
	{
		int num;
		cin >> num;
		if (num == 0) T = NULL;
		else
		{
			T = new TreeNode(num);
			preCreate(T->left);
			preCreate(T->right);
		}
	}

	void preOrder(TreeNode* T)
	{
		if (T == NULL) return; 
		else
		{
			cout << T->val << "  ";
			preOrder(T->left);
			preOrder(T->right);
		}
	}
};
int main()
{
	
	Solution so;
	TreeNode *T1;
	TreeNode *T2;
	vector<int> vec;

	cout << "创建T1:" << endl;
	so.preCreate(T1);
	cout << "创建T1成功！" << endl;



	cout << "T1的前序遍历:" << endl;
	so.preOrder(T1);
	cout << endl;

	vec = so.PrintFromTopToBottom(T1);

	cout << "层次遍历的结果是:" << endl;
	for (auto it = vec.begin();it != vec.end();it++)
		cout << *it << "  ";


	
	
	cout << endl;
	return 0;
}