TL;DR

On with TASK #2 from The Weekly Challenge #195. Enjoy!

The challenge

You are given a list of numbers, @list.

Write a script to find most frequent even numbers in the list. In case you get more than one even numbers then return the smallest even integer. For all other case, return -1.

Example 1

Input: @list = (1,1,2,6,2)
Output: 2 as there are only 2 even numbers 2 and 6 and of those 2 
appears the most.

Example 2

Input: @list = (1,3,5,7)
Output: -1 since no even numbers found in the list

Example 3

Input: @list = (6,4,4,6,1)
Output: 4 since there are only two even numbers 4 and 6. They both
appears the equal number of times, so pick the smallest.

The questions

Should we only consider positive integers? By the way, are integers the only suitable numbers?

The solution

The algorithm in this case will be very basic: iterate through the provided list, keeping track of the best candidate as the list goes on.

We can track the amount of each even number with a slot in a hash, so that we can land on the most frequent.

Perl goes first this time:

#!/usr/bin/env perl
use v5.24;
use warnings;
use experimental 'signatures';
no warnings 'experimental::signatures';

my @list = @ARGV ? @ARGV : qw< 1 1 2 6 2 >;

my $result = -1;
my $result_count = 0;
my %count_for = (-1 => 0);
for my $item (@list) {
   next if $item % 2;
   my $current = $count_for{$item}++;
   ($result, $result_count) = ($item, $current)
      if $current > $result_count
      || ($current == $result_count && $item < $result);
}
say $result;

The translation into Raku is pretty straightforward:

#!/usr/bin/env raku
use v6;
sub MAIN (*@args) {
   my @list = @args ?? @args !! < 1 1 2 6 2 >».Int;
   my $result = -1;
   my $result_count = 0;
   my %count_for = -1 => 0;
   for @list -> $item {
      next if $item % 2;
      my $current = %count_for{$item}++;
      ($result, $result_count) = $item, $current
         if $current > $result_count
         || ($current == $result_count && $item < $result);
   }
   put $result;
}

Enough for today… stay safe!