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Co-authored-by: Andrii Siriak <siryaka@gmail.com>
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Others/Damm.java
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113
Others/Damm.java
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package Others;
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import java.util.Objects;
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/**
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* Damm algorithm is a check digit algorithm that detects all single-digit errors
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* and all adjacent transposition errors. It was presented by H. Michael Damm in 2004.
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* Essential part of the algorithm is a quasigroup of order 10
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* (i.e. having a 10 × 10 Latin square as the body of its operation table)
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* with the special feature of being weakly totally anti-symmetric.
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* Damm revealed several methods to create totally anti-symmetric quasigroups
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* of order 10 and gave some examples in his doctoral dissertation.
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*
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* @see <a href="https://en.wikipedia.org/wiki/Damm_algorithm">Wiki. Damm algorithm</a>
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*/
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public class Damm {
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/**
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* Weakly totally anti-symmetric quasigroup of order 10.
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* This table is not the only possible realisation of weak totally anti-symmetric
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* quasigroup but the most common one (taken from Damm doctoral dissertation).
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* All zeros lay on the diagonal because it simplifies the check digit calculation.
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*/
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private static final byte[][] DAMM_TABLE = {
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{0, 3, 1, 7, 5, 9, 8, 6, 4, 2},
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{7, 0, 9, 2, 1, 5, 4, 8, 6, 3},
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{4, 2, 0, 6, 8, 7, 1, 3, 5, 9},
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{1, 7, 5, 0, 9, 8, 3, 4, 2, 6},
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{6, 1, 2, 3, 0, 4, 5, 9, 7, 8},
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{3, 6, 7, 4, 2, 0, 9, 5, 8, 1},
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{5, 8, 6, 9, 7, 2, 0, 1, 3, 4},
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{8, 9, 4, 5, 3, 6, 2, 0, 1, 7},
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{9, 4, 3, 8, 6, 1, 7, 2, 0, 5},
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{2, 5, 8, 1, 4, 3, 6, 7, 9, 0}
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};
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/**
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* Check input digits by Damm algorithm.
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*
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* @param digits input to check
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* @return true if check was successful, false otherwise
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* @throws IllegalArgumentException if input parameter contains not only digits
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* @throws NullPointerException if input is null
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*/
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public static boolean dammCheck(String digits) {
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checkInput(digits);
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int[] numbers = toIntArray(digits);
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int checksum = 0;
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for (int number : numbers) {
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checksum = DAMM_TABLE[checksum][number];
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}
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return checksum == 0;
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}
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/**
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* Calculate check digit for initial digits and add it tho the last position.
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*
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* @param initialDigits initial value
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* @return digits with the checksum in the last position
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* @throws IllegalArgumentException if input parameter contains not only digits
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* @throws NullPointerException if input is null
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*/
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public static String addDammChecksum(String initialDigits) {
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checkInput(initialDigits);
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int[] numbers = toIntArray(initialDigits);
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int checksum = 0;
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for (int number : numbers) {
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checksum = DAMM_TABLE[checksum][number];
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}
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return initialDigits + checksum;
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}
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public static void main(String[] args) {
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System.out.println("Damm algorithm usage examples:");
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var validInput = "5724";
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var invalidInput = "5824";
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checkAndPrint(validInput);
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checkAndPrint(invalidInput);
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System.out.println("\nCheck digit generation example:");
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var input = "572";
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generateAndPrint(input);
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}
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private static void checkAndPrint(String input) {
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String validationResult = Damm.dammCheck(input)
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? "valid"
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: "not valid";
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System.out.println("Input '" + input + "' is " + validationResult);
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}
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private static void generateAndPrint(String input) {
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String result = addDammChecksum(input);
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System.out.println("Generate and add checksum to initial value '" + input + "'. Result: '" + result + "'");
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}
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private static void checkInput(String input) {
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Objects.requireNonNull(input);
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if (!input.matches("\\d+")) {
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throw new IllegalArgumentException("Input '" + input + "' contains not only digits");
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}
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}
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private static int[] toIntArray(String string) {
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return string.chars()
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.map(i -> Character.digit(i, 10))
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.toArray();
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}
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}
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