面试题21：从上往下打印二叉树

代码：

#include "stdafx.h"
#include <iostream>
#include <deque>
using namespace std;

struct BinaryTreeNode
{
	int m_nValue;
	BinaryTreeNode *m_pLeft;
	BinaryTreeNode *m_pRight;
};

void PrintFromTopToDown(BinaryTreeNode *pRoot)
{
	if (pRoot == NULL)
	{
		return;
	}

    deque<BinaryTreeNode *> myDeque;
	myDeque.push_back(pRoot);
	while (!myDeque.empty())
	{
        BinaryTreeNode *pTop = myDeque.front();
		cout << pTop->m_nValue << " ";
		myDeque.pop_front();

		if (pTop->m_pLeft != NULL)
		{
			myDeque.push_back(pTop->m_pLeft);
		}

		if (pTop->m_pRight != NULL)
		{
			myDeque.push_back(pTop->m_pRight);
		}
	}
}

//以先序的方式构建二叉树，输入-1表示结点为空
void CreateBinaryTree(BinaryTreeNode *&pRoot)
{
	int nNodeValue = 0;
	cin >> nNodeValue;	
	if (-1 == nNodeValue)
	{
		return; 
	}
	else
	{
		pRoot = new BinaryTreeNode();
		pRoot->m_nValue = nNodeValue;
		CreateBinaryTree(pRoot->m_pLeft);
		CreateBinaryTree(pRoot->m_pRight);
	}
}

void PrintInOrder(BinaryTreeNode *&pRoot)
{
	if (pRoot != NULL)
	{
		PrintInOrder(pRoot->m_pLeft);
		cout << pRoot->m_nValue << " ";
		PrintInOrder(pRoot->m_pRight);
	}
}

int _tmain(int argc, _TCHAR* argv[])
{
	BinaryTreeNode *pRoot = NULL;
	CreateBinaryTree(pRoot);
	PrintInOrder(pRoot);
	cout << endl;
    PrintFromTopToDown(pRoot);
	cout << endl;
	system("pause");
	return 0;
}