Array median

You are given two sorted arrays. Write a script to merge the two given sorted arrays and return the median of the merged array.

Examples

Example 1
Input: @arr1 = (2), @arr2 = (4)
Output: 3.0
Merged array: (2,4)
Median: (2+4)/2 => 3

Example 2
Input: @arr1 = (1,2,3), @arr2 = (7,8,9,10)
Output: 7.0
Merged array: (1,2,3,7,8,9,10)
Length of merged array is 7, the 4th element is 7.

Example 3
Input: @arr1 = (), @arr2 = (10,20,30,40)
Output: 25.0
Merged array: (10,20,30,40)
Median: (20+30)/2 => 25

Example 4
Input: @arr1 = (100), @arr2 = (1,2,3,4,5,6,7)
Output: 4.5
Merged array: (1,2,3,4,5,6,7,100)
Median: (4+5)/2 => 4.5

Example 5
Input: @arr1 = (1,2,2), @arr2 = (2,2,3)
Output: 2.0
Merged array: (1,2,2,2,2,3)
Median: (2+2)/2 => 2

Analysis

No doubt someone will have a one-liner for this, but I prefer the more readable answer. In any case, the easy way to do this is to concatenate the arrays, sort the result and then:

• if the result is odd in length, the median is the middle element of the merged array,
• or if it's even, the median is the mean of the two middle entries

In his post, Peter takes an impressively straightforward approach that prioritises the clarity of coding instead of extreme conciseness of the code. His approach uses simple array concatenation and arithmetic checking of the index for median computation as well as there is a thorough input/output reporting that facilitates understanding of the logic.

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

Try it 

Your input:

@arr1 =

eg: 1, 2, 3

@arr2 =

eg: 4, 5, 6, 7

⤡

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2026-09-14
use utf8;     # Week 391 - task 1 - Array median
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';
use Encode;

array_median([2], [4]);
array_median([1, 2, 3], [7, 8, 9, 10]);
array_median([], [10, 20, 30, 40]);
array_median([100], [1, 2, 3, 4, 5, 6, 7]);
array_median([1, 2, 2], [2, 2, 3]);

sub array_median {
    
    my (@merged, $middle, $median);
    
    # merge, sort and count arrays
    push @merged, @{$_[$_]} for 0 .. 1;
    @merged = sort {$a <=> $b} @merged;
    $middle = @merged / 2 - 1;
    
    # even number of entries
    if ($middle == int($middle)) {
        $median = ($merged[$middle] + $merged[$middle + 1]) / 2;
        
    # odd number of entries
    } else {
        $median = ($merged[$middle + 1]);
    }
    
    # report
    say qq[\nInput:  \@arr1 = (] . join(', ', @{$_[0]}) .
        '), @arr2 = (' . join(', ', @{$_[1]}) . ')';
    say qq[Output: $median];
}

12 lines of code

Output from script

Input:  @arr1 = (2), @arr2 = (4)
Output: 3

Input:  @arr1 = (1, 2, 3), @arr2 = (7, 8, 9, 10)
Output: 7

Input:  @arr1 = (), @arr2 = (10, 20, 30, 40)
Output: 25

Input:  @arr1 = (100), @arr2 = (1, 2, 3, 4, 5, 6, 7)
Output: 4.5

Input:  @arr1 = (1, 2, 2), @arr2 = (2, 2, 3)
Output: 2