laurent_r

These are some answers to the Week 100 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Task 1: Fun Time

You are given a time (12 hour / 24 hour).

Write a script to convert the given time from 12 hour format to 24 hour format and vice versa.

Ideally we expect a one-liner.

Example 1:

Input: 05:15 pm or 05:15pm
Output: 17:15

Example 2:

Input: 19:15
Output: 07:15 pm or 07:15pm

Well, I like concise code, but I don’t think it makes real sense to try to pack this task into a one-liner. I have no doubt that it can be done, but it will either be not a real one-liner (like a pipeline chaining multiple statements into one expression), or a difficult to understand golfing attempt. So, I will not try to do a one-liner.

Fun Time in Raku

We use a regex to detect whether the input string matches “am” or “pm”; if so, we remove that “am” or “pm” string and add 12 hours if the matched string was “pm”; otherwise, we subtract 12 from the hour part it if is larger than 12 and add “pm” or “am” depending on the case.

use v6;

my $time = @*ARGS[0];
if $time ~~ /(<[ap]>)m/ {
    if $0 eq 'a'  {
        $time ~~ s/(\d\d':'\d\d).*/$0/;
    } else {
        $time ~~ s/(\d\d)':'(\d\d).*/{$0 + 12}:$1/;
    }
} else {
    $time ~~ /^(\d\d)':'(\d\d)/;
    my ($suffix, $hour) = $0 > 12 ?? ('pm', $0 - 12) !! ('am', $0);
    $time = "$hour:$1 $suffix";
}
say $time;

These are some execution examples with various input strings:

$ raku fun-time.raku '10:54'
10:54 am
-
$ raku fun-time.raku '17:54'
5:54 pm
-
$ raku fun-time.raku '10:54 pm'
22:54
-
$ raku fun-time.raku '10:54 am'
10:54

Fun Time in Perl

This is a port to Perl of the Raku program just above:

use strict;
use warnings;
use feature "say";

my $time = shift;
if ($time =~ /([ap])m/) {
    if ($1 eq 'a')  {
        $time =~ s/(\d\d:\d\d).*/$1/;
    } else {
        $time =~ /(\d\d):(\d\d.).*/;
        my $hour = $1 + 12;
        $time = "$hour:$2";
    }
} else {
    $time =~ /^(\d\d):(\d\d)/;
    my ($suffix, $hour) = $1 > 12 ? ('pm', $1 - 12) : ('am', $1);
    $time = "$hour:$2 $suffix";
}
say $time;

And some execution examples:

$ perl fun-time.pl '10:54 pm'
22:54

$ perl fun-time.pl '10:54 am'
10:54

$ perl fun-time.pl '10:54'
10:54 am

$ perl fun-time.pl '15:54'
3:54 pm

Task 2: Triangle Sum

You are given triangle array.

Write a script to find the minimum path sum from top to bottom.

When you are on index i on the current row then you may move to either index i or index i + 1 on the next row.

Example 1:

Input: Triangle = [ [1], [2,4], [6,4,9], [5,1,7,2] ]
Output: 8

Explanation: The given triangle

            1
           2 4
          6 4 9
         5 1 7 2

The minimum path sum from top to bottom:  1 + 2 + 4 + 1 = 8

             [1]
           [2]  4
           6 [4] 9
          5 [1] 7 2

Example 2:

Input: Triangle = [ [3], [3,1], [5,2,3], [4,3,1,3] ]
Output: 7

Explanation: The given triangle

            3
           3 1
          5 2 3
         4 3 1 3

The minimum path sum from top to bottom: 3 + 1 + 2 + 1 = 7

             [3]
            3  [1]
           5 [2] 3
          4 3 [1] 3

Triangle Sum in Raku

We use the traverse recursive subroutine to find the smallest path through the triangular array:

use v6;

my @triangle = (1), (2,4), (6,4,9), (5,1,7,2);
my @min-path = map { $_[0] }, @triangle; # pick any path
my $min-path-val = @min-path.sum;
my $index = 0;
traverse @triangle, (), $index;
say @min-path;

sub traverse (@triangle, @path, $index) {
    my @first-line = @triangle[0];
    my @new-triangle = @triangle[1 .. @triangle.end];
    say "First-line: ", @first-line;
    my @new-path = | (@path, @first-line[$index]);
    say @new-path, "  ", "\n";
    if @new-triangle.elems > 0 {
        traverse(@new-triangle, @new-path, $index);
        traverse(@new-triangle, @new-path, $index + 1);
    } else {
        my $new-path-val = @new-path.sum;
        if $new-path-val < $min-path-val {
            @min-path = @new-path;
            $min-path-val = $new-path-val
        }
    }
}

Output:

$ raku triangle-sum.raku 1 2 4 1

Triangle Sum in Perl

Except for the fact that we define also a sum subroutine, this essentially the same Raku algorithm ported to Perl:

use strict;
use warnings;
use feature "say";

my $triangle = [ [1], [2,4], [6,4,9], [5,1,7,2] ];
# $triangle = [ [1], [2,4], [6,30,9], [30,30,30,2] ];
my $min_path = [ map { $_->[0] } @$triangle];
my $min_path_val = sum($min_path);
my $index = 0;
find_min_path($triangle, [], $index);
say "@$min_path";

sub sum {
    my $aref = shift;
    my $sum = 0;
    $sum += $_ for @$aref;
    return $sum;
}

sub find_min_path {
    my ($tri_ref, $path, $index) = @_;
    my @triangle = @$tri_ref;
    my @first_row = @{$triangle[0]};
    my @new_triangle = @triangle[1 .. $#triangle];
    my $new_path = [ @$path, $first_row[$index] ];
    if (@new_triangle) {
        find_min_path([@new_triangle], $new_path , $index);
        find_min_path([@new_triangle], $new_path, $index + 1);
    } else { 
        my $new_path_val = sum($new_path);
        if ($new_path_val < $min_path_val) {
            $min_path = $new_path;
            $min_path_val = $new_path_val;
        }
    }
}

Output with the above input data:

$ perl  triangle-sum.pl
1 2 4 1

If you uncomment the second triangle definition, you get the following output:

$ perl  triangle-sum.pl
1 4 9 2

Wrapping up

The next week Perl Weekly Challenge will start soon. If you want to participate in this challenge, please check https://perlweeklychallenge.org/ and make sure you answer the challenge before 23:59 BST (British summer time) on Sunday, February 28, 2021. And, please, also spread the word about the Perl Weekly Challenge if you can.