Print the binary tree from top to bottom and print the binary tree from bottom to bottom.

Print the binary tree from top to bottom and print the binary tree from bottom to bottom.
Question: each node of the binary tree is printed from top to bottom, and the nodes on the same layer are printed from left to right.

Idea: If a node has a subnode every time a node is printed, the subnode of the node is placed at the end of a queue. Next, retrieve the first node in the queue from the queue header and repeat the previous print operation until all nodes in the queue are printed.

  1 #include "stdafx.h"  2 #include<stdio.h>  3 #include<deque>  4 #include<tchar.h>  5   6 struct BinaryTreeNode  7 {  8     int              m_nValue;  9     BinaryTreeNode*  m_pLeft; 10     BinaryTreeNode*  m_pRight; 11 }; 12  13 BinaryTreeNode* CreateBinaryTreeNode(int value) 14 { 15     BinaryTreeNode* pNode = new BinaryTreeNode(); 16     pNode->m_nValue = value; 17     pNode->m_pLeft = NULL; 18     pNode->m_pRight = NULL; 19 } 20  21 void ConnectTreeNodes(BinaryTreeNode* pParent, BinaryTreeNode* pLeft,  22                     BinaryTreeNode* pRight) 23 { 24     if(pParent != NULL) 25     { 26         pParent->m_pLeft = pLeft; 27         pParent->m_pRight = pRight; 28     } 29 } 30  31 void PrintTreeNode(BinaryTreeNode* pNode) 32 { 33     if(pNode != NULL) 34     { 35         printf("value of this node is: %d\n", pNode->m_nValue); 36          37         if(pNode->m_pLeft != NULL) 38             printf("value of its left child is: %d.\n", pNode->m_pLeft->m_nValue); 39         else 40             printf("left child is null.\n"); 41          42         if(pNode->m_pRight != NULL) 43             printf("value of its right child is: %d.\n",pNode->m_pRight->m_nValue); 44         else 45             printf("right child is null.\n"); 46     } 47     else 48     { 49         printf("this node is null.\n"); 50     } 51     printf("\n"); 52 } 53  54 void PrintTree(BinaryTreeNode* pRoot) 55 { 56     PrintTreeNode(pRoot); 57      58     if(pRoot != NULL) 59     { 60         if(pRoot->m_pLeft != NULL) 61             PrintTree(pRoot->m_pLeft); 62          63         if(pRoot->m_pRight != NULL)  64             PrintTree(pRoot->m_pRight); 65     } 66 } 67  68 void DestroyTree(BinaryTreeNode* pRoot) 69 { 70     if(pRoot != NULL) 71     { 72         BinaryTreeNode* pLeft = pRoot->m_pLeft; 73         BinaryTreeNode* pRight = pRoot->m_pRight; 74          75         delete pRoot; 76         pRoot = NULL; 77          78         DestroyTree(pLeft); 79         DestroyTree(pRight); 80     } 81 } 82  83  84 void PrintFromTopToBottom(BinaryTreeNode* pRoot) 85 { 86     if(pRoot == NULL) 87         return; 88          89     std::deque<BinaryTreeNode *> dequeTreeNode; 90      91     dequeTreeNode.push_back(pRoot); 92      93     while(dequeTreeNode.size()) 94     { 95         BinaryTreeNode *pNode = dequeTreeNode.front(); 96         dequeTreeNode.pop_front(); 97          98         printf("%d ", pNode->m_nValue); 99         100         if(pNode->m_pLeft)101             dequeTreeNode.push_back(pNode->m_pLeft);102         103         if(pNode->m_pRight)104             dequeTreeNode.push_back(pNode->m_pRight);105     }106 }107 108 //            10109 //         /      \110 //        6        14111 //       /\        /\112 //      4  8     12  16113 114 int main()115 {116     BinaryTreeNode* pNode10 = CreateBinaryTreeNode(10);117     BinaryTreeNode* pNode6  = CreateBinaryTreeNode(6);118     BinaryTreeNode* pNode14 = CreateBinaryTreeNode(14);119     BinaryTreeNode* pNode4  = CreateBinaryTreeNode(4);120     BinaryTreeNode* pNode8  = CreateBinaryTreeNode(8);121     BinaryTreeNode* pNode12 = CreateBinaryTreeNode(12);122     BinaryTreeNode* pNode16 = CreateBinaryTreeNode(16);123     124     ConnectTreeNodes(pNode10, pNode6, pNode14);125     ConnectTreeNodes(pNode6, pNode4, pNode8);126     ConnectTreeNodes(pNode14, pNode12, pNode16);127     128     PrintTree(pNode10);129     130     printf("The nodes from top to bottom, from left to right are: \n");131     PrintFromTopToBottom(pNode10);132     133     printf("\n\n");134 }