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sub distance (Str $first, Str $second) {
    my int $m = $first.chars;
    my int $n = $second.chars;

    # distance matrix: ($m+1) x ($n+1) of integers
    my @d;
    @d[$_][0] = $_ for 0..$m;   # deletion costs
    @d[0][$_] = $_ for 0..$n;   # insertion costs

    # Pre‑extract characters as integers (faster than repeated .comb)
    my @s = $first.ords;
    my @t = $second.ords;

    loop (my int $i = 1; $i <= $m; $i++) {
        my int $s_i = @s[$i-1];
        loop (my int $j = 1; $j <= $n; $j++) {
            if $s_i == @t[$j-1] {
                @d[$i][$j] = @d[$i-1][$j-1];
            } else {
                # Raku's built‑in min is concise and still fast for short strings
                @d[$i][$j] = 1 + min(
                    @d[$i-1][$j],   # deletion
                    @d[$i][$j-1],   # insertion
                    @d[$i-1][$j-1]  # substitution
                );
            }
        }
    }

    @d[$m][$n];
}

use Test;

plan 15;   # we will run 15 test cases

# Each test is: (string A, string B, expected_distance)
my @test_cases =
    # Empty strings
    ("",      "",      0),
    ("",      "a",     1),
    ("",      "ab",    2),
    ("a",     "",      1),
    ("ab",    "",      2),

    # Single character
    ("a",     "a",     0),
    ("a",     "b",     1),
    ("a",     "aa",    1),
    ("aa",    "a",     1),

    # Two characters
    ("ab",    "ab",    0),
    ("ab",    "ac",    1),    # substitution
    ("ab",    "a",     1),    # deletion
    ("ab",    "cab",   1),    # insertion at front

    # Longer strings
    ("kitten","sitting",3),
    ("saturday","sunday",3);

for @test_cases -> ($a, $b, $expected) {
    my $got = distance($a, $b);
    is $got, $expected, "distance('$a', '$b') == $expected";
}