The Damm algorithm is a checksum algorithm which detects all single digit errors and adjacent transposition errors.



The algorithm is named after H. Michael Damm.



Task

Verify the checksum, stored as last digit of an input.



import std.stdio;
 
auto 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],
];
 
bool damm(string s) {
    int interim = 0;
    foreach (c; s) {
        interim = table[interim][c - '0'];
    }
    return interim == 0;
}
 
void main() {
    import std.conv : to;
    auto numbers = [5724, 5727, 112946, 112949];
    foreach (number; numbers) {
        bool isValid = damm(number.to!string());
        writef("%6d is ", number);
        if (isValid) {
            writeln("valid");
        } else {
            writeln("invalid");
        }
    }
}