problem 41

/*
We shall say that an n-digit number is pandigital if it makes use of all the digits 1 to n exactly once. For example, 2143 is a 4-digit pandigital and is also prime.

What is the largest n-digit pandigital prime that exists?
*/

#include <iostream>
#include<math.h>
#include<vector>
#include <algorithm>  
#include<set>
using namespace std;

bool is_prime(int num){
  if (num % 2 == 0){
    return false;
  }
 for(int i = 3; i <= ceil(sqrt(num)); i+= 2){
   if(num % i == 0){
     return false;
   }
 }
 return true;
}

int main() {
  vector<int> primes;
  string str = "1234567";
 while( std::next_permutation(str.begin() , str.end()) ){
   int convert = stoi(str);
   if(is_prime(convert)){
     primes.push_back(convert);
   }
  }
  cout << primes[primes.size() - 1];
 return 0;
}