Application of C / C ++ tree traversal - Rebuilding tree

Input:
    Line input binary number of nodes in
    the node numbering sequence preorder Before entering the second row, separated by a space adjacent numbered
    node in the input sequence preorder number, line 3, numbers separated by a space adjacent

Output:
    After output of a row of nodes in preorder number sequence, separated by a space

Code

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

int n, pos;
vector<int> pre, in, post;

void rec(int l, int r){
	if(l >= r) return;
	int root = pre[pos++];
	int m = distance(in.begin(), find(in.begin(), in.end(), root));
	rec(l, m);
	rec(m+1, r);
	post.push_back(root);
}

void solve(){
	pos = 0;
	rec(0, pre.size());
	for(int i = 0; i < n; i++){
		if(i) cout << " ";
		cout << post[i];
	}
	cout << endl;
}

int main(){
	int k;
	cin >> n;
	for(int i = 0; i < n; i++){
		cin >> k;
		pre.push_back(k);
	}
	
	for(int i = 0; i < n; i++){
		cin >> k;
		in.push_back(k);
	}
	
	solve();
}