Divisible average

You are given an array of positive integers. Write a script to return the closest integer to the mean value of all even integers that are divisible by 3. If none is divisible, return 0.

Examples

Example 1
Input: @arr = (18, 5, 7, 11)
Output: 18
18 is the only even number and divisible by 3.
Average: 18 / 1 = 18.

Example 2
Input: @arr = (6, 12, 18, 24, 30, 40)
Output: 18
The qualifying numbers are 6, 12, 18, 24, and 30.
Average: (6 + 12 + 18 + 24 + 30) / 5 = 90 / 5 = 18

Example 3
Input: @arr = (3, 9, 15, 21, 27)
Output: 0
None of the elements are even.
Since no elements qualify, return 0.

Example 4
Input: @arr = (6, 12, 14, 20)
Output: 9
The qualifying numbers are 6 and 12.
Average: (6 + 12) / 2 = 9.

Example 5
Input: @arr = (6, 6, 6, 12, 12)
Output: 8
All five numbers are even and divisible by 3.
Average: (6 + 6 + 6 + 12 + 12) / 5 = 8.4 => 8

Analysis

An easy challenge with not much to do other than follow the instructions. The edge case where no integers are multiples of 6 is easily handled.

I completed this challenge on my Android phone on a moving train using AndFTP, QuickEdit and Termius. I was pleasantly surprised to find that QuickEdit can execute a Perl script, apparently on the phone.

The post for the Weekly Challenge presents a brilliant but simple Perl script that does the filtering as well as the mean-rounding in a few lines. It also has a great mechanism for dealing with edge cases when criteria is missing while providing an excellent mobile development experience using terminal as well as text editor.

This review may cover either or both challenges for this week.

Try it 

Your input:

#!/usr/bin/perl

# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge/398/1

use v5.26;    # The Weekly Challenge - 2026-11-02
use utf8;     # Week 398 - task 1 - Divisible average
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';
use Encode;

divisible_average(18, 5, 7, 11);
divisible_average(6, 12, 18, 24, 30, 40);
divisible_average(3, 9, 15, 21, 27);
divisible_average(6, 12, 14, 20);
divisible_average(6, 6, 6, 10, 12);

sub divisible_average {
    
    my (@array, @sixes, $sum, $result);
    
    # initialise    
    @array = @_;
    
    # extract multiples of 6
    @sixes = grep {$_ / 6 == int($_ / 6)} @array;

    # sum and rounded average
    if (@sixes) {
        $sum += $_ for @sixes;
        $result = int($sum / @sixes + 0.5);
    }
    
    # report
    say qq[\nInput:  (] . join(', ', @array) . ')';
    say qq[Output: ] . ($result or 0);
}

9 lines of code

Output from script

Input:  (18, 5, 7, 11)
Output: 18

Input:  (6, 12, 18, 24, 30, 40)
Output: 18

Input:  (3, 9, 15, 21, 27)
Output: 0

Input:  (6, 12, 14, 20)
Output: 9

Input:  (6, 6, 6, 10, 12)
Output: 8