【目標】

建立如下所示的一棵二叉樹，並且輸出其對應的前序遍歷、中序遍歷、後序遍歷。

【程式碼實現】

建立二叉樹以及實現遍歷的操作存放在Binarytree.h檔案中

//Binarytree.h
#ifndef Binarytree_H
#define Binarytree_H
template<class T> class Binarytree;
template<class T>
class TreeNode
{
    friend class Binarytree<T>;
private:
    T data;
    TreeNode<
 
T> *rchild;    //右指標指向右子樹
    TreeNode<T> *lchild;   //左指標指向左子樹
};
template<class T>
class Binarytree
{
public:
    Binarytree(){root=0;};
    void CreatTree();  //根據實際情況建立二叉樹
    void Preorder();
    void Preorder(TreeNode<T> *currentnode); //前序遍歷

    void Inorder();
    void Inorder(TreeNode<
 
T> *currentnode); //中序遍歷

    void Postorder();
    void Postorder(TreeNode<T> *currentnode); //後序遍歷
private:
    TreeNode<T> *root;
};
//-------建立二叉樹--------
template<class T>
void  Binarytree<T>::CreatTree()
{
  TreeNode<T> *p1=new TreeNode<T>();
  p1->data='A';
  p1->
 
rchild=0;
  p1->lchild=0;
  root=p1;


  TreeNode<T> *p2=new TreeNode<T>();
  p2->data='B';
  p2->rchild=0;
  p2->lchild=0;
  root->lchild=p2;


  TreeNode<T> *p3=new TreeNode<T>();
  p3->data='C';
  p3->rchild=0;
  p3->lchild=0;
  root->rchild=p3;


  TreeNode<T> *p4=new TreeNode<T>();
  p4->data='D';
  p4->rchild=0;
  p4->lchild=0;
  root->lchild->lchild=p4;


  TreeNode<T> *p5=new TreeNode<T>();
  p5->data='E';
  p5->rchild=0;
  p5->lchild=0;
  root->lchild->rchild=p5;


  TreeNode<T> *p6=new TreeNode<T>();
  p6->data='F';
  p6->rchild=0;
  p6->lchild=0;
  root->rchild->lchild=p6;


  TreeNode<T> *p7=new TreeNode<T>();
  p7->data='G';
  p7->rchild=0;
  p7->lchild=0;
  root->rchild->rchild=p7;

  TreeNode<T> *p8=new TreeNode<T>();
  p8->data='H';
  p8->rchild=0;
  p8->lchild=0;
  root->lchild->lchild->lchild=p8;


  TreeNode<T> *p9=new TreeNode<T>();
  p9->data='I';
  p9->rchild=0;
  p9->lchild=0;
  root->lchild->lchild->rchild=p9;

}
//------遞迴實現二叉樹的前序遍歷------
template<class T>
void  Binarytree<T>::Preorder() 
{  
    cout<<"前序遍歷（根->左->右）為：";
    Preorder(root); 
}
template<class T>
void  Binarytree<T>::Preorder(TreeNode<T> *currentnode)
{
  if(currentnode)
  {
    cout<<currentnode->data<<" ";
    Preorder(currentnode->lchild);
    Preorder(currentnode->rchild);
  }
}

//------遞迴實現二叉樹的中序遍歷------
template<class T>
void  Binarytree<T>::Inorder() 
{  
    cout<<"中序遍歷（左->根->右）為：";
    Inorder(root); 
}
template<class T>
void  Binarytree<T>::Inorder(TreeNode<T> *currentnode)
{
  if(currentnode)
  {
    Inorder(currentnode->lchild);
    cout<<currentnode->data<<" ";
    Inorder(currentnode->rchild);
  }
}

//------遞迴實現二叉樹的後序遍歷------
template<class T>
void  Binarytree<T>::Postorder() 
{  
    cout<<"後序遍歷（左->右->根）為：";
    Postorder(root); 
}
template<class T>
void  Binarytree<T>::Postorder(TreeNode<T> *currentnode)
{
  if(currentnode)
  {
    Postorder(currentnode->lchild);
    Postorder(currentnode->rchild);
    cout<<currentnode->data<<" ";
  }
}
#endif

主程式：

//main.cpp
#include "Binarytree.h"
#include <iostream>
using namespace std;
int main()
{
  Binarytree<char> Tree1;
  Tree1.CreatTree();
  Tree1.Preorder();
  cout<<endl;
  Tree1.Inorder();
  cout<<endl;
  Tree1.Postorder();
  cout<<endl;
  system("pause");
  return 0;
}

【結果圖】