## Perl Weekly Challenge 276: Maximum Frequency

These are some answers to the Week 276, Task 2, of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in a few days from now (on July 7, 2024 at 23:59). This blog post provides some solutions to this challenge. Please don’t read on if you intend to complete the challenge on your own.

## Task 2: Maximum Frequency

You are given an array of positive integers, `@ints`.

Write a script to return the total number of elements in the given array which have the highest frequency.

Example 1

``````Input: @ints = (1, 2, 2, 4, 1, 5)
Ouput: 4

The maximum frequency is 2.
The elements 1 and 2 has the maximum frequency.
``````

Example 2

``````Input: @ints = (1, 2, 3, 4, 5)
Ouput: 5

The maximum frequency is 1.
The elements 1, 2, 3, 4 and 5 has the maximum frequency.
``````

### Maximum Frequency in Raku

We use a Bag to store the frequencies. This is very simple because we just need to coerce the input array to a `Bag` in order to compute the various frequencies. Then, we compute the maximum frequency and finally count the items whose frequency is equal to the maximum frequency.

``````sub max-frequency (@in) {
my \$frequencies = @in.Bag;
my \$max = \$frequencies.values.max;
my \$count = 0;
for \$frequencies.keys -> \$i {
\$count += \$max if \$frequencies{\$i} == \$max;
}
return \$count;
}

my @tests = (1, 2, 2, 4, 1, 5), (1, 2, 3, 4, 5);
for @tests -> @test {
printf "%-15s => ", "@test[]";
say max-frequency @test;
}
``````

This program displays the following output:

``````\$  raku ./max-frequency.raku
1 2 2 4 1 5     => 4
1 2 3 4 5       => 5
``````

### Maximum Frequency in Perl

This is a port to Perl of the above Raku program. Perl having no `Bags`, we use a hash instead, but we need an explicit `for` loop to compute the frequencies and populate the `%frequencies` hash. Similarly, we need a `for` loop to compute the maximum frequency.

``````use strict;
use warnings;
use feature 'say';

sub max_frequency {
my %frequencies;
for my \$i (@_) {
\$frequencies{\$i}++;
}                                                                                                                       `
my \$max = 0;
for my \$i (values %frequencies) {
\$max = \$i if \$i > \$max;
}
my \$count = 0;
for my \$i (keys %frequencies) {
\$count += \$max if \$frequencies{\$i} == \$max;
}
return \$count;
}

my @tests = ( [1, 2, 2, 4, 1, 5], [1, 2, 3, 4, 5]);
for my \$test (@tests) {
printf "%-15s => ", "@\$test";
say max_frequency @\$test;
}
``````

This program displays the following output:

``````\$ perl  ./max-frequency.pl
1 2 2 4 1 5     => 4
1 2 3 4 5       => 5
``````

## 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 July 14, 2024. And, please, also spread the word about the Perl Weekly Challenge if you can.