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);
}
private int BruteForce(int numDigits)
{
var range = new EulerRange((int)Math.Pow(10, numDigits - 1), (int)Math.Pow(10, numDigits) - 1);
var numbers = new List <(int left, int right, int total)>();
//Get every multiple
foreach (var item in range)
{
numbers.AddRange(range.Select(x => (x, item, item * x)));
}
foreach (var item in numbers.OrderByDescending(x => x.total))
{
if (NumberStringHelper.IsNumberPalindrome(item.total))
{
return(item.total);
}
}
return(-1);
}
public void NumberIsPalindromTest(int attempt, bool expected)
{
var result = NumberStringHelper.IsNumberPalindrome(attempt);
Assert.AreEqual(expected, result);
}
