private int OptimizationAttempt1(int numDigits)
{
if (numDigits == 1)
{
return(9);
}
var upperLimit = (int)Math.Pow(10, numDigits) - 1;
var lowerLimit = upperLimit - (int)Math.Pow(10, numDigits - 1);
var range = new EulerRange(lowerLimit, upperLimit);
HashSet <int> numbers = new HashSet <int>();
//Get every multiple
foreach (var item in range)
{
range.Select(x => numbers.Add(item * x)).ToList();
}
foreach (var item in numbers.OrderByDescending(x => x))
{
if (NumberStringHelper.IsNumberPalindrome(item))
{
return(item);
}
}
return(-1);
}
