二叉树及基本操作

二叉树的基本概念：

二叉树的每个结点最多只有两个孩子结点，也就是说每个结点最多有两个子树。
二叉树有 5 种基本形态：
（1）空二叉树，树为空，没有结点；（2）只有根结点的二叉树；(3)只有左子树的二叉树；(4)只有右子树的二叉树；(5)左右子树都有的二叉树。

#include<iostream>
using namespace std;
class Node {
public:
    int data;
    Node *lchild, *rchild;
    Node(int _data) {
        data = _data;
        lchild = NULL;
        rchild = NULL;
    }
    ~Node() {
        if (lchild != NULL) {
            delete lchild;
        }
        if (rchild != NULL) {
            delete rchild;
        }
    }
**//-----------先序遍历----------**
    void preorder() {
        cout << data << " ";
        if (lchild != NULL) {
            lchild->preorder();
        }
        if (rchild != NULL) {
            rchild->preorder();
        }
    }
**//-----------中序遍历----------**
    void inorder() {
        if (lchild != NULL) {
            lchild->inorder();
        }
        cout << data << " ";
        if (rchild != NULL) {
            rchild->inorder();
        }
    }
**//-----------后序遍历---------------**
        void postorder() {
        if (lchild != NULL) {
            lchild->postorder();
        }

        if (rchild != NULL) {
            rchild->postorder();
        }
             cout << data << " ";
    }

};
class BinaryTree {
private:
    Node *root;
public:
    BinaryTree() {
        root = NULL;
    }
    ~BinaryTree() {
        if (root != NULL) {
            delete root;
        }
    }
    void build_demo() {
        root = new Node(1);
        root->lchild = new Node(2);
        root->rchild = new Node(3);
        root->lchild->lchild = new Node(4);
        root->lchild->rchild = new Node(5);
        root->rchild->rchild = new Node(6);
    }
    void preorder() {
        root->preorder();
    }
    void inorder() {
        root->inorder();
    }
     void postorder() {
        root->postorder();
    }
};
int main() {
    BinaryTree binarytree;
    binarytree.build_demo();
    binarytree.preorder();
    cout << endl;
    binarytree.inorder();
    cout << endl;
      binarytree.postorder();
    cout << endl;
    return 0;
}