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;}