題目：樹的遍歷！按先序遍歷建立一棵樹，分別以先序、中序、後序遍歷輸出

樣例輸入

A B # D # # C E # # F # #

樣例輸出

PreOrder: A B D C E F
InOrder: B D A E C F
PostOrder: D B E F C A

程式碼：

//按先序遍歷建立一棵樹，分別以先序、中序、後序遍歷輸出
#include <iostream>
using namespace std;

struct node{
	char ch;
	node *left, *right;
};

node* creat() {
	node *root = new node;
	char c;
	cin >> c;
	if(c == '#') root = NULL;
	else {
		root->ch = c;
		root->left = creat();
		root->right = creat();
	}
	return root;
}

void preOrder(node *root) {
	if(root == NULL)  return;       //這條語句不能忘！！！
	cout << " " << root->ch;
	preOrder(root->left);
	preOrder(root->right);
}

void inOrder(node *root) {
	if(root == NULL)  return;
	inOrder(root->left);
	cout << " " << root->ch;
	inOrder(root->right);
}

void postOrder(node *root) {
	if(root == NULL)  return;
	postOrder(root->left);
	postOrder(root->right);
	cout << " " << root->ch;
}

int main() {
	node *root = creat();
	cout << "preOrder:";
	preOrder(root);
	cout << endl;
	cout << "inOrder:";
	inOrder(root);
	cout << endl;
	cout << "postOrder:";
	postOrder(root);
	cout << endl;
	return 0;
}