/// <summary>
/// Determines equality between a number and the sum
/// of the factorials of each of its digits.
/// </summary>
/// <param name="number"></param>
/// <returns></returns>
public bool NumberEqualsSumOfDigitFactorials(int number)
{
var split = DigitHelper.SplitDigits(number);
int sum = split.Sum(num => GetFactorial(num));
return(sum == number);
}
/// <summary>
/// Returns whether the number
/// contains 1-9 exactly once and is 9 digits long.
/// </summary>
/// <param name="number"></param>
/// <returns></returns>
public bool IsPandigital(int number)
{
// create 10 booleans to represent 0-9.
// for each digit, set the index of that digit
// to true. If any are false, then it is not pandigital.
// 0 is set to true because it is not included.
// first, check to see if we have 9 digits.
if (DigitHelper.DigitCount(number) != DigitLength)
{
return(false);
}
int temp = number;
bool[] nums = new bool[10];
nums[0] = true;
while (temp > 0)
{
int n = temp % 10; // get the next digit
nums[n] = true;
temp /= 10; // so we can grab the next digit next time
}
return(nums.All(n => n));
}
/// <summary>
/// Returns whether a number is pandigital to its own digit count,
/// such that 2143 is pandigital to 4 digits.
/// </summary>
/// <param name="number"></param>
/// <returns></returns>
public bool IsPandigitalToOwnDigitCount(int number)
{
int digitCount = DigitHelper.DigitCount(number);
bool[] nums = new bool[digitCount + 1];
nums[0] = true;
int temp = number;
while (temp > 0)
{
int n = temp % 10;
if (n > digitCount)
{
return(false); // it can't be pandigital is you have a 6 in a 5 digit number.
}
nums[n] = true;
temp /= 10;
}
return(nums.All(n => n));
}
public bool IsPandigital(int multiplicand, int multiplier, int product)
{
var concat = DigitHelper.Concat(DigitHelper.Concat(multiplicand, multiplier), product);
return(IsPandigital(concat));
}