Task — Complete day

You are given an array of integers, @hours. Write a script to return the number of pairs that forms a complete day. A complete day is defined as a time duration that is an exact multiple of 24 hours.

Examples

Example 1
Input: @hours = (12, 12, 30, 24, 24)
Output: 2
Pair 1: (12, 12)
Pair 2: (24, 24)

Example 2
Input: @hours = (72, 48, 24, 5)
Output: 3
Pair 1: (72, 48)
Pair 2: (72, 24)
Pair 3: (48, 24)

Example 3
Input: @hours = (12, 18, 24)
Output: 0

Analysis

The obvious way to do this is simply two nested loops covering all possible pairs and checking whether they sum to a multiple of 24, so that's what I did.

Even with 1000 random integers - so half a million possible pairs - it takes under a second on my machine to find the 20847 qualifying pairs.

Try it 

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2024-07-01
use utf8;     # Week 276 - task 1 - Complete day
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';

my (@hours);

complete_day(12, 12, 30, 24, 24);
complete_day(72, 48, 24, 5);
complete_day(12, 18, 24);

push @hours, int(rand(30)) for 0 .. 24;
complete_day(@hours);

sub complete_day {
    
    my (@hours, $pairs, $a, $b, $days, $explain);
    
    @hours = @_;
    
    # loop over all pairs
    $pairs = 0;
    $explain = '';
    for $a (0 .. @hours - 2) {
        for $b ($a + 1 .. @hours - 1) {
            
            # determine if this pair sums to a whole number of days
            $days = ($hours[$a] + $hours[$b]) / 24; 
            next unless (int($days) == $days);
            $pairs ++;
            $explain .= qq[($hours[$a] + $hours[$b]), ];
        }
    }
    printf(qq[\nInput:  \@hours = (%s)\n], join(', ', @hours));
    printf(qq[Output: %s: %s\n], $pairs, substr($explain, 0, -2));
}

Output

Input:  @hours = (12, 12, 30, 24, 24)
Output: 2: (12 + 12), (24 + 24)

Input:  @hours = (72, 48, 24, 5)
Output: 3: (72 + 48), (72 + 24), (48 + 24)

Input:  @hours = (12, 18, 24)
Output: 0:

Input:  @hours = (27, 1, 23, 21, 16, 14, 25, 25, 2, 22, 
  11, 25, 14, 8, 0, 13, 17, 14, 6, 17, 13, 15, 5, 25, 12)
Output: 10: (27 + 21), (1 + 23), (23 + 25), (23 + 25), 
  (23 + 25), (23 + 25), (16 + 8), (2 + 22), (11 + 13), 
  (11 + 13)