RogerBW's Blog

I’ve been doing the Weekly Challenges. The latest involved list searching and directory evaluation. (Note that this is open until 12 February 2023.)

Task 1: Special Quadruplets

You are given an array of integers.

Write a script to find out the total special quadruplets for the given array.

Special Quadruplets are such that satisfies the following 2 rules.

1. nums[a] + nums[b] + nums[c] == nums[d]
2. a < b < c < d

So this is basically the same pattern as challenges 187 part 2 and 188 part 1, similarly without any possibilities of short-cuts to avoid inner loops. Some languages have a readily-accessible combinations generator; others don't.

Raku:

sub specialquads(@l) {
  my $ct = 0;
  for @l.combinations(4) -> @c {
    if (@c[0] + @c[1] + @c[2] == @c[3]) {
      $ct++;
    }
  }
  return $ct;
}

PostScript:

/specialquads {
    5 dict begin
    /l exch def
    0
    0 1 l length 4 sub {
        /ai exch def
        ai 1 add 1 l length 3 sub {
            /bi exch def
            bi 1 add 1 l length 2 sub {
                /ci exch def
                ci 1 add 1 l length 1 sub {
                    /di exch def
                    l ai get l bi get add l ci get add l di get eq {
                        1 add
                    } if
                } for
            } for
        } for
    } for
    end
} bind def

Task 2: Copy Directory

You are given path to two folders, $source and $target.

Write a script that recursively copy the directory from $source to $target except any files.

In other words, replicate the directory structure. I only felt enthusiasm for this in Perl and Raku: Perl using File::Find:

sub copydir($src, $dst) {
  my @ds;
  my $l = 1 + length($src);
  find(sub{
         if (-d $_) {
           push @ds,substr($File::Find::name, $l);
         }
       }, $src);
  foreach my $d (@ds) {
    if (defined $d && length($d) > 0) {
      mkdir "$dst/$d";
    }
  }
}

and Raku using recursion:

sub getdirs($src) {
    my @a;
    for dir($src) -> $e {
        if ($e.d) {
            @a.push($e);
            @a.append(getdirs($e))
        }
    }
    return @a;
}

sub copydir($src, $dst) {
    my $l = 1 + $src.chars;
    for map {$_.substr($l)}, getdirs($src) -> $o {
        mkdir "$dst/$o";
    }
}

Full code on github.