后10个点全部mle，想不出别的优化了求助大佬QAQ

#include<bits/stdc++.h>
using namespace std;

int n , k;
vector<string> x = {"0" , "1"};

int main()
{
   cin >> n >> k;
   for(int i = 0;i < n - 1;i ++)
     {            
      vector<string> a , b , t;    
      for(int j = 0;j < x.size();j ++)
         a.push_back ("0" + x[j]);      
         
      for(int u = x.size() - 1;u >= 0;u --)
         b.push_back("1" + x[u]);      

 t.insert(t.end() , a.begin() , a.end());
 t.insert(t.end() , b.begin() , b.end());
            
 x = t;
 }
    cout << x[k];
    return 0;
}