Binary search tree from preorder to preorder and postorder

First , To understand that the preamble sequence of a binary search tree can uniquely determine a binary search tree .

First step , Establish root node （ The first value of the sequence ）

The second step , Get the offset of the first node of the right subtree k（ Used to divide the interval ）

The third step , Divide the interval of left and right subtrees

#include<iostream>
#include<vector>
using namespace std;
typedef struct Node* Tree;
const int N = 1010;
vector<int> hx,qx,zx;
int a[N];
struct Node{
	int data;
	Tree l,r;
	Node(int _data){
		data = _data;
		l = r = nullptr;
	}
};
// l Is the beginning of the sequence ,sz Is the size of the sequence 
void build(int l,int sz,Tree &tree){
	if(sz <= 0) return;
	tree = new Node(a[l]);
	int k = 1;
	while(l+k < sz && a[l+k] < a[l]) k++;
	qx.push_back(tree->data);
	build(l+1,k-1,tree->l);
	zx.push_back(tree->data);	
	build(l+k,sz-k,tree->r);
	hx.push_back(tree->data);
}

int main(){
	int n;
	cin>>n;
	for(int i = 0; i < n; i++) cin>>a[i];
	Tree root = nullptr;
	build(0,n,root); 
	cout<<" The first sequence traversal ："; 
	for(auto num:qx) cout<<num<<' ';
	cout<<"\n In the sequence traversal ：";
	for(auto num:zx) cout<<num<<' ';
	cout<<"\n After the sequence traversal ：";
	for(auto num:hx) cout<<num<<' ';
	return 0;
}
/*
7
8 6 5 7 10 8 11
*/