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;
}

 

 

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