BLOG: The Weekly Challenge #064

Saturday, Jun 20, 2020| Tags: Perl, Raku


This weekly blog is coming a week later than normal. Why? Last week I tried Live Coding for the first time. It was scary but enjoyable experience. It took more time than the blog. Having said that I didn’t want to stop blogging about my solutions. So here you go, I am sharing my solutions with you. Just for record, please find below links to the Live Coding videos.

Live Coding: Perl

Live Coding: Raku

If you have seen my earlier blogs, you must have noticed the patter I follow normally i.e. solve the challenge in Perl and then translate the same into Raku. This time, I had tough time translating solution to Minimum Sum Path into Raku. Generally it is pain free but for some reason it wasn’t giving the expected result. In the end, I gave up as I was running short of time. Most of my Raku trouble, I rely on the Gang of Raku experts available on the official Twitter handle @PerlWChallenge. I have been lucky so far till date to get detailed response. I did post the question on Twitter and request for help. Unfortunately, I haven’t heard anything so far. So the solution is still pending. For this reason, I didn’t submit the Raku solution. I would be grateful if you could find the issue in this Raku solution.

Let me share my solutions to the Perl Weekly Challenge - 064.

TASK #1 › Minimum Sum Path

Submitted by Mohammad S Anwar

Reviewed by Ryan Thompson

Given an m × n matrix with non-negative integers, write a script to find a path from top left to bottom right which minimizes the sum of all numbers along its path. You can only move either down or right at any point in time.

Below is the core sub find_path() that does most of the work. I relied on recursive logic to deal with it. I commented the code appropriately for anyone reading it.

sub find_path {
    my ($matrix, $row, $col, $path) = @_;
    $path = [] unless defined $path;

    my $rows = $#$matrix;
    my $cols = $#{$matrix->[0]};

    # check boundary?
    return if ($row > $rows || $col > $cols);

    my $final_path = [ @$path ];
    push @$final_path, $matrix->[$row][$col];

    # reached bottom right corner?
    return $final_path if ($row == $rows && $col == $cols);

    my @current_path = ();

    # go right if possible.
    push @current_path, find_path($matrix, $row, $col + 1, $final_path);

    # go down if possible.
    push @current_path, find_path($matrix, $row + 1, $col, $final_path);

    return @current_path;

Now once we have figured out all possible routes from the top left corner to the bottom right corner, it is time to find the minimum sum path. For this I came up with the following sub min_sum_path().

sub min_sum_path {
    my ($matrix, $row, $col, $path) = @_;

    my $paths = {};
    $paths->{join " →  ", @$_} = sum @$_ for find_path($matrix, 0, 0);
    return (sort {  $paths->{$a} <=> $paths->{$b} } keys %$paths)[0];

This is my unsuccessfull attempt of translating the above sub find_path(). If look at it carefully, I am not doing anything extravagant here, just line by line translation, but still not getting the desired result for some strange reason.

sub find-path(Array[] $matrix, Int $row, Int $col, @path? = ()) {

    my $rows = $matrix.elems - 1;
    my $cols = $matrix.[0].elems - 1;

    # check boundary?
    return @path if $row > $rows || $col > $cols;

    my @final-path = @path.[];
    @final-path.push: $matrix.[$row][$col];

    if ($row == $rows && $col == $cols) {
        dd @final-path;

    # reached bottom right corner?
    return @final-path if $row == $rows && $col == $cols;

    my @current-path = ();

    # go right if possible.
    @current-path.push: find-path($matrix, $row, $col + 1, @final-path);

    # go down if possible.
    @current-path.push: find-path($matrix, $row + 1, $col, @final-path);

    return @current-path;

Below is the standalone Perl solution to the Minimum Sum Path task dealing with the given matrix in the task.

use List::Util qw(sum);

my $matrix = [[ 1, 2, 3 ],
              [ 4, 5, 6 ],
              [ 7, 8, 9 ]];

print min_sum_path($matrix, 0, 0), "\n";

Similary, here is the unit test script for the same.

use Test::More;
use List::Util qw(sum);

is(min_sum_path([[ 1, 2, 3 ],
                 [ 4, 5, 6 ],
                 [ 7, 8, 9 ]],
                 0, 0),
   "1 →  2 →  3 →  6 →  9");


TASK #2 › Word Break

Submitted by Mohammad S Anwar

Reviewed by Ryan Thompson

You are given a string $S and an array of words @W.

Write a script to find out if $S can be split into sequence of one or more words as in the given @W.

Print the all the words if found otherwise print 0.

Generally the Task #2 tends to be harder than the Task #1. But for the Week #064, it was the other way round, at least for me. If you look at the code sub word_break() then you would agree with me.

sub word_break {
    my ($string, $words) = @_;

    my $matched = [ grep { $string =~ /$_/i } @$words ];
    return [0] unless scalar @$matched;

    my $search_order = {};
    foreach my $word (@$matched) {
        $search_order->{index($string, $word)} = $word;

    return [
        map  { $search_order->{$_} }
        sort { $a <=> $b } keys %$search_order

I enjoyed getting the Raku solution for the above Perl solution. I no longer have to look at the notes, thanks to the weekly challenge. Having said, I still learn something new every week. So what did I learn this time? I learnt how to sort hash key numerially. As you know, by default hash key sort alphabetically. Fot this task, I wanted to sort the hash key numerically. A quick google lookup and I had the answer as noted below.

sub word-break(Str $string, @words where .all ~~ Str) {

    my @matched = @words.grep: -> $word { $string ~~ / $word / };
    return 0 unless @matched.elems;

    my %search-order =
        -> $word { $string.index($word) => $word });

    return [
        %search-order.keys.sort({ $^a <=> $^b })
        .map({ %search-order{$_} })

Time to get the standalone Perl app.

my $string = "perlweeklychallenge";
my $words  = [ "weekly", "challenge", "perl" ];
my $match  = word_break($string, $words);

print sprintf("%s\n", join (", ", @$match));

The equivalent Raku standalone app as below.

sub MAIN(Str :$string = "perlweeklychallenge",
         :@words where .all ~~ Str = ("weekly", "challenge", "perl")) {

    word-break($string, @words).join(", ").say;

Unit test in Perl goes like this.

use Test::More;
use Test::Deep;

is_deeply(word_break("perlweeklychallenge", [ "weekly", "challenge", "perl" ]),
          [ "perl", "weekly", "challenge" ], "match test");
is_deeply(word_break("perlandraku", [ "python", "ruby", "haskell" ]),
          [ 0 ], "no match test");


And Raku unit test is even cleaner.

use Test;

is word-break("perlweeklychallenge", [ "weekly", "challenge", "perl" ]),
   [ "perl", "weekly", "challenge" ],
   "match test";

is word-break("perlandraku", [ "python", "ruby", "haskell" ]),
   "no match test";


That’s it for this week. Speak to you soon.


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