Luhn Algorithm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 | public static class LuhnAlgorithm { /// number:620000011408893661 /// checkdigit:1 public static bool IsValid(string number, char checkdigit) { return checkdigit.ToString() == CalculateCheckdigit(number).ToString(); } public static byte CalculateCheckdigit(string number) { var numbers = number .Reverse() .ToList() .ConvertAll(ConvertCharToInt32); for (var i = 0; i < numbers.Count; i += 2) { var n = numbers[i]; n *= 2; if (n > 9) { var subNumbers = n .ToString() .ToList() .ConvertAll(ConvertCharToInt32); n = subNumbers.Sum(); } numbers[i] = n; } // Sum var sumNumbers = numbers.Sum(); // Subtract var nextDec = Math.Ceiling((decimal)sumNumbers / 10) * 10; var result = Convert.ToByte(nextDec - sumNumbers); return result; } private static Int32 ConvertCharToInt32(char number) { int n; return Int32.TryParse(number.ToString(), out n) ? n : default(Int32); } } |