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  • 【面试题023】从上往下打印二叉树

    【面试题023】从上往下打印二叉树 

    层次遍历二叉树就是队列的应用

     

    树是图的一种特殊退化形式，从上到下按层次遍历二叉树，从本质上来说就是广度优先遍历二叉树。

    PrintTree.cpp:

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    #include <iostream>
    #include <cstdio>
    #include <deque>
    #include "BinaryTree.h"

    using namespace std;

    void PrintFromTopToBottom(BinaryTreeNode *pTreeRoot)
    {
        if(!pTreeRoot)
        {
            return;
        }
        deque<BinaryTreeNode *> dequeTreeNode;

        dequeTreeNode.push_back(pTreeRoot);
        while(dequeTreeNode.size())
        {
            BinaryTreeNode *pNode = dequeTreeNode.front();
            dequeTreeNode.pop_front();

            printf("%d ", pNode->m_nValue);

            if(pNode->m_pLeft)
            {
                dequeTreeNode.push_back(pNode->m_pLeft);
            }
            if(pNode->m_pRight)
            {
                dequeTreeNode.push_back(pNode->m_pRight);
            }
        }
    }

    //            10
    //         /      
    //        6        14
    //       /        /
    //      4  8     12  16
    int main()
    {
        BinaryTreeNode *pNode10 = CreateBinaryTreeNode(10);
        BinaryTreeNode *pNode6 = CreateBinaryTreeNode(6);
        BinaryTreeNode *pNode14 = CreateBinaryTreeNode(14);
        BinaryTreeNode *pNode4 = CreateBinaryTreeNode(4);
        BinaryTreeNode *pNode8 = CreateBinaryTreeNode(8);
        BinaryTreeNode *pNode12 = CreateBinaryTreeNode(12);
        BinaryTreeNode *pNode16 = CreateBinaryTreeNode(16);

        ConnectTreeNodes(pNode10, pNode6, pNode14);
        ConnectTreeNodes(pNode6, pNode4, pNode8);
        ConnectTreeNodes(pNode14, pNode12, pNode16);

        BinaryTreeNode *pRoot = pNode10;
        PrintTree(pRoot);

        printf("The nodes from top to bottom, from left to right are:  ");
        PrintFromTopToBottom(pRoot);
        cout << endl;
        DestroyTree(pNode10);

        return 0;
    }

    BinaryTree.h:

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    #ifndef _BINARY_TREE_H_
    #define _BINARY_TREE_H_

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

    BinaryTreeNode *CreateBinaryTreeNode(int value);
    void ConnectTreeNodes(
        BinaryTreeNode *pParent,
        BinaryTreeNode *pLeft, BinaryTreeNode *pRight);
    void PrintTreeNode(BinaryTreeNode *pNode);
    void PrintTree(BinaryTreeNode *pRoot);
    void DestroyTree(BinaryTreeNode *pRoot);


    #endif /*_BINARY_TREE_H_*/

     

    BinaryTree.cpp:

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    #include <iostream>
    #include <cstdio>
    #include "BinaryTree.h"

    using namespace std;
    BinaryTreeNode *CreateBinaryTreeNode(int value)
    {
        BinaryTreeNode *pNode = new BinaryTreeNode();
        pNode->m_nValue = value;
        pNode->m_pLeft = NULL;
        pNode->m_pRight = NULL;

        return pNode;
    }

    void ConnectTreeNodes(
        BinaryTreeNode *pParent,
        BinaryTreeNode *pLeft,
        BinaryTreeNode *pRight)
    {
        if(pParent != NULL)
        {
            pParent->m_pLeft = pLeft;
            pParent->m_pRight = pRight;
        }
    }

    void PrintTreeNode(BinaryTreeNode *pNode)
    {
        if(pNode != NULL)
        {
            printf("value of this node is: %d ", pNode->m_nValue);

            if(pNode->m_pLeft != NULL)
                printf("value of its left child is: %d. ",
                       pNode->m_pLeft->m_nValue);
            else
                printf("left child is null. ");

            if(pNode->m_pRight != NULL)
                printf("value of its right child is: %d. ",
                       pNode->m_pRight->m_nValue);
            else
                printf("right child is null. ");
        }
        else
        {
            printf("this node is null. ");
        }

        printf(" ");
    }

    void PrintTree(BinaryTreeNode *pRoot)
    {
        PrintTreeNode(pRoot);

        if(pRoot != NULL)
        {
            if(pRoot->m_pLeft != NULL)
                PrintTree(pRoot->m_pLeft);

            if(pRoot->m_pRight != NULL)
                PrintTree(pRoot->m_pRight);
        }
    }

    void DestroyTree(BinaryTreeNode *pRoot)
    {
        if(pRoot != NULL)
        {
            BinaryTreeNode *pLeft = pRoot->m_pLeft;
            BinaryTreeNode *pRight = pRoot->m_pRight;

            delete pRoot;
            pRoot = NULL;

            DestroyTree(pLeft);
            DestroyTree(pRight);
        }
    }
     

    Makefile:

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    .PHONY:clean  
    CPP=g++  
    CFLAGS=-Wall -g  
    BIN=test  
    OBJS=PrintTree.o BinaryTree.o  
    LIBS=  
    $(BIN):$(OBJS)  
        $(CPP) $(CFLAGS) $^ -o $@ $(LIBS)  
    %.o:%.cpp  
        $(CPP) $(CFLAGS) -c $< -o $@  
    clean:  
        rm -f *.o $(BIN)  


    运行结果:

    value of this node is: 10
    value of its left child is: 6.
    value of its right child is: 14.
    value of this node is: 6
    value of its left child is: 4.
    value of its right child is: 8.
    value of this node is: 4
    left child is null.
    right child is null.
    value of this node is: 8
    left child is null.
    right child is null.
    value of this node is: 14
    value of its left child is: 12.
    value of its right child is: 16.
    value of this node is: 12
    left child is null.
    right child is null.
    value of this node is: 16
    left child is null.
    right child is null.
    The nodes from top to bottom, from left to right are:
    10 6 14 4 8 12 16
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  • 原文地址：https://www.cnblogs.com/codemylife/p/3722738.html
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