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

Try it 

Your input:

#!/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