C++二叉树的建立、前序、中序、后序遍历

最近在LintCode上练习算法，感觉对数据结构的体用Python或者Java写起来都很费劲，像二叉树这种数据结构，Python是Java都用对象进行封装实现的，感觉有点浪费，还是用C++写起来比较顺手，不过好久不用C++，好多都忘 了，所以在这里记录一下，免得再忘 了，还不知道去哪里找。

二叉树是数据结构里最觉的一种了，重要性不言而喻。

#include<iostream>using namespace std;struct TreeNode{    char data;    struct TreeNode *lchild, *rchild;};struct TreeNode* T;//struct TreeNode R;void creat_binary_tree(TreeNode* &T);void pre_order(TreeNode *T);void mid_order(TreeNode *T);void post_order(TreeNode *T);int main(){    while (true)    {        int select_index = 0;        cout << "(1)创建一棵新树" << endl;        cout << "(2)前序遍历" << endl;        cout << "(3)中序遍历" << endl;        cout << "(4)后序遍历" << endl;        cout << "(5)退出系统" << endl;        cout << "请选择需要的操作：" ;        cin >> select_index;        switch(select_index)        {        case 1:            cout << "创建一颗树，其中A->Z字符代表树的数据，用”#“表示空树:" << endl;            creat_binary_tree(T);            break;        case 2:            cout << "前序遍历:" << endl;            pre_order(T);            cout << '\n' << endl;            break;        case 3:            cout << "中序遍历:" << endl;            mid_order(T);            cout << '\n' << endl;            break;        case 4:            cout << "后序遍历:" << endl;            post_order(T);            cout << '\n' << endl;            break;        case 5:            return 0;            break;        default:            cout << "输入有误，请重新输入：<< endl" ;        }    }    return 0;}void creat_binary_tree(TreeNode* &T){    char ch;    cin >> ch;    if(ch == '#')        T = NULL;    else    {        T = new TreeNode;        T->data = ch;        creat_binary_tree(T->lchild);        creat_binary_tree(T->rchild);    }}void pre_order(TreeNode *T){    if(T)    {        cout << T->data << "  " ;        pre_order(T->lchild);        pre_order(T->rchild);    }}void mid_order(TreeNode *T){    if(T)    {        mid_order(T->lchild);        cout << T->data << "  " ;        mid_order(T->rchild);    }}void post_order(TreeNode *T){    if(T)    {        post_order(T->lchild);        post_order(T->rchild);        cout << T->data << "  " ;    }}