public string Solve()
{
var primes = new HashSet <int>(new Primes(10000).PrimeList().Where(x => x > 1000));
var matching = new List <int>();
foreach (var prime in primes)
{
if (matching.Contains(prime))
{
continue;
}
var ps = Combinatorics.PermuteForward(prime.ToString().ToArray())
.Select(y => int.Parse(new string(y)))
.Where(y => primes.Contains(y))
.ToList();
ps.Sort();
if (ps.Count() >= 3 && !ps.Contains(1487) && ps[1] + (ps[1] - ps[0]) == ps[2])
{
matching.AddRange(ps);
}
}
return(string.Join("", matching.OrderBy(x => x).Select(x => x.ToString())));
}
public string Solve()
{
var answer = Combinatorics.PermuteForward(_digits)
.Where(x => x[0] != '0' && DivisibilityTest(x))
.Select(x => long.Parse(new string(x.ToArray())))
.Sum();
return(answer.ToString());
}
private IEnumerable <IList <char> > PandigitalPermutations()
{
return(Combinatorics.PermuteForward(new [] { '1', '2', '3', '4', '5', '6', '7', '8', '9' }));
}