RogerBW's Blog

I’ve been doing the Weekly Challenges. The latest involved string replacement and character searching. (Note that this ends today.)

Task 1: Defrang IP Address

You are given a valid IPv4 address.

Write a script to return the defranged version of the given IP address.

A defranged IP address replaces every period "." with "[.]".

I have no idea why you'd want to do this, but fair enough. There are two basic approaches depending on the language: either a global substitution (with regular expressions where ndeeded, though they don't make this particular problem any easier) or digging a little deeper with a character-by-character processing loop.

Raku, global substitution:

sub defrangip($a) {
    (my $b = $a) ~~ s:g/\./[.]/;
    return $b;
}

Rust, a processing loop (also PostScript):

(There is in fact a replace() method for String types in Rust, I had just already written this before I thought of looking for it.)

fn defrangip(a: &str) -> String {
    let mut out = String::new();
    for c in a.chars() {
        if c == '.' {
            out.push_str("[.]");
        } else {
            out.push(c);
        }
    }
    out
}

Task 2: String Score

You are given a string, $str.

Write a script to return the score of the given string.

The score of a string is defined as the sum of the absolute difference between the ASCII values of adjacent characters.

Also pretty straightforward. Perl doesn't have an "overlapping chunks of an array" function, so I do it with indices (Ditto Lua.).

sub stringscore($a) {
  my $out = 0;
  my @c = split '',$a;
  foreach my $i (0 .. $#c - 1) {
    $out += abs(ord($c[$i]) - ord($c[$i+1]));
  }
  return $out;
}

Everything else does, or can have it added, even PostScript now that I've written a rotor method inspired by Raku's.

/stringscore {
    0 exch
    s2a
    2 -1 rotor
    {
        aload pop sub abs add
    } forall
} bind def

Full code on github.