public static HashSet <long> Generate(int nDigit)
{
var numbers = Enumerable.Range(1, nDigit);
var numberString = string.Empty;
foreach (var number in numbers)
{
numberString += number;
}
return(Permutations.Generate(long.Parse(numberString)));
}
public static HashSet <long> GenerateZeroToN(int nDigit)
{
var numbers = Enumerable.Range(1, nDigit).ToList();
//append 0 at end so cast to long doesn't chop it off
numbers.Add(0);
var numberString = string.Empty;
foreach (var number in numbers)
{
numberString += number;
}
var pandigitals = Permutations.Generate(long.Parse(numberString));
//remove any permutations that begin with 0, gets removed in the cast
//and therefore isn't a 0 - n pandigital.
pandigitals.RemoveWhere(p => p.ToString().Length != nDigit + 1);
return(pandigitals);
}
public override long Solve()
{
for (int number = 1490; number < 9999; number++)
{
var perms = Permutations.Generate(number).Where(p => p.ToString().Length == 4);
var permsList = new List <long>();
perms.ToList().ForEach(p => { if (Primes.IsPrime(p))
{
permsList.Add(p);
}
});
if (permsList.Count >= 4)
{
var sequence = FindSequence(permsList);
if (sequence.Count > 0 && !sequence.Contains(1487))
{
return(long.Parse(sequence[0].ToString() + sequence[1].ToString() + sequence[2].ToString()));
}
}
}
throw new Exception("Cannot find sequence....you messed it up");
}