class DammAlgorithm { private static final int[][] TABLE = [ [0, 3, 1, 7, 5, 9, 8, 6, 4, 2], [7, 0, 9, 2, 1, 5, 4, 8, 6, 3], [4, 2, 0, 6, 8, 7, 1, 3, 5, 9], [1, 7, 5, 0, 9, 8, 3, 4, 2, 6], [6, 1, 2, 3, 0, 4, 5, 9, 7, 8], [3, 6, 7, 4, 2, 0, 9, 5, 8, 1], [5, 8, 6, 9, 7, 2, 0, 1, 3, 4], [8, 9, 4, 5, 3, 6, 2, 0, 1, 7], [9, 4, 3, 8, 6, 1, 7, 2, 0, 5], [2, 5, 8, 1, 4, 3, 6, 7, 9, 0], ] private static boolean damm(String s) { int interim = 0 for (char c : s.toCharArray()) interim = TABLE[interim][c - ('0' as Character)] return interim == 0 } static void main(String[] args) { int[] numbers = [5724, 5727, 112946, 112949] for (Integer number : numbers) { boolean isValid = damm(number.toString()) if (isValid) { System.out.printf("%6d is valid\n", number) } else { System.out.printf("%6d is invalid\n", number) } } } }