#include<iostream>
#include<vector>
using namespace std;

struct TreeNode
{
	int val;
	TreeNode* left, *right;
	TreeNode(int x) :val(x), left(NULL), right(NULL){}
};
void BST_insert(TreeNode* node, TreeNode* insert_node)
{
	if(insert_node->val < node->val)
	{
		if(node->left)
			BST_insert(node->left, insert_node);
		else
			node -> left = insert_node;
	}
	else{
		if(node->right)
			BST_insert(node->right, insert_node);
		else
			node->right = insert_node;
	}
}

void preorder(TreeNode* node, int layer)
{
	if(node == nullptr)
		return;
	for(int i = 0; i < layer; ++i)
		printf("----");
	printf("[%d]\n", node->val);
	preorder(node->left, layer + 1);
	preorder(node->right, layer + 1);
}

int main()
{
	TreeNode root(8);
	vector<TreeNode*> node_vec;
	int test[] = { 3, 10, 1, 6, 15 };
	for(int i = 0; i < 5; ++i)
		node_vec.push_back(new TreeNode(test[i]));

	for(int i = 0; i < 5; ++i)
		BST_insert(&root, node_vec[i]);

	preorder(&root, 0);

	return 0;
}