不断找新的先序的根节点，根据位置切割中序，根据中序左右子树大小反切割先序，找到左子树对应的先序中序，然后递归处理

#include<stdio.h>
#include<vector>
#include<map>
#include<algorithm>
#include <algorithm>
#include <iostream>
#include<string>
using namespace std;
#define ll long long
//# define int long long
#define ull unsigned long long
#define pii pair<int,int>

#define baoliu(x, y) cout << fixed << setprecision(y) << x
#define endl  "\n"
#define debug1(x) cerr<<"x"<<" "
#define  debug2(x) cerr<<"x"<<endl
const int N = 2e5 + 10;
const int M = 1e6 + 10;
const int inf = 0x3f3f3f3f;
const int mod = 998244353;
const double eps = 1e-8;
int n, m;
int a[N];
void dfs(string pre,string mid){
	//if(pre.size()==1)
	if(pre.empty())return ;
	int idx=mid.find(pre[0]);
	
	
	//左子树
	dfs(pre.substr(1,idx),mid.substr(0,idx));
	//右子树
	dfs(pre.substr(idx+1),mid.substr(idx+1));
	cout<<pre[0];
}
void solve(){
	string pre,mid;
	cin>>pre>>mid;
	dfs(pre,mid);
}
int main() {
    cin.tie(0);
    
    ios::sync_with_stdio(false);

    int t;
   //cin>>t;
     t=1;
    while (t--) {
solve();
    }
    return 0;
}