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day 38
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day 38
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#include <set>
#include <iostream>
#include <algorithm>
int main()
{
// precomputation step 1:
// find all primes below sqrt(987654321)
std::set<unsigned int> smallPrimes;
smallPrimes.insert(2);
for (unsigned int i = 3; i*i <= 987654321; i += 2)
{
bool isPrime = true;
for (auto p : smallPrimes)
{
// abort, no divisors possible
if (p*p > i)
break;
// divisor found ?
if (i % p == 0)
{
isPrime = false;
break;
}
}
// found a prime number
if (isPrime)
smallPrimes.insert(i);
}
// precomputation step 2:
// generate all permutations of the strings "12", "123", "1234", ..., "123456789"
// and test whether they are prime
std::set<unsigned int> panPrimes;
for (unsigned int digits = 2; digits <= 9; digits++)
{
std::string strNumber = "123456789";
// reduce number of digits
strNumber.erase(digits);
do
{
unsigned int number = std::stoi(strNumber);
// test whether pandigital number is prime
bool isPrime = true;
for (auto p : smallPrimes)
{
// abort, no divisors possible
if (p*p > number)
break;
// divisor found ?
if (number % p == 0)
{
isPrime = false;
break;
}
}
// found a pandigital prime ?
if (isPrime)
panPrimes.insert(number);
} while (std::next_permutation(strNumber.begin(), strNumber.end()));
}
// process input
unsigned int tests;
std::cin >> tests;
while (tests--)
{
unsigned int limit;
std::cin >> limit;
// find next larger pandigital prime number
auto i = panPrimes.upper_bound(limit);
// smaller than the smallest pandigital prime ?
if (i == panPrimes.begin())
{
std::cout << "-1" << std::endl;
continue;
}
// upper_bound() goes one step too far
i--;
// and print it
std::cout << *i << std::endl;
}
return 0;
}