2-1-2-2

非常简单的前序遍历，建树使用递归算法

#include<stdio.h>
#include<stdlib.h>

struct node;
typedef struct node* A;

struct node
{
	int data;
	A left;
	A right;
};

A insert(A node,int num);
void pre(A Tree);
void pre(A Tree)
{
	if(Tree)
	{
		printf("%d,",Tree->data);
		pre(Tree->left);
		pre(Tree->right);
	}
}

A insert(A node,int num)
{
	if(node==NULL)
	{
		node=(A)malloc(sizeof(A));
		node->data=num;
		node->left=node->right=NULL;
	}
	else
	{
		if(num<node->data)
		{
			node->left=insert(node->left,num);
		}
		if(num>node->data)
		{
			node->right=insert(node->right,num);
		}
	}
	return node;
}

int main()
{
	int a=-1;
	A B=NULL;
	scanf("%d,",&a);
	while(a!=-1)
	{
		B=insert(B,a);
		a=-1;
		scanf("%d,",&a);
	}
	pre(B);
	return 0;
}