public class DammCheckDigit { private static final int[][] damm = { {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 is_valid(Integer num) { char[] n = num.toString().toCharArray(); int temp = 0; for (char ch : n) { temp = damm[temp][ch - '0']; } return temp == 0; } public static void main(String[] args) { System.out.printf("%s", "Valid numbers between 5700 and 5800 are:"); for(int i = 5700; i <= 5800; i++) { if (is_valid(i)) System.out.printf("%d ", i); } System.out.printf("%s", "\n"); } }