Task — Double exist

You are given an array of integers, @ints. Write a script to find if there exist two indices $i and $j such that:

1. $i != $j
2. 0 <= ($i, $j) < scalar @ints
3. $ints[$i] == 2 * $ints[$j]

Examples

Example 1
Input: @ints = (6, 2, 3, 3)
Output: true
For $i = 0, $j = 2
$ints[$i] = 6 => 2 * 3 =>  2 * $ints[$j]

Example 2
Input: @ints = (3, 1, 4, 13)
Output: false

Example 3
Input: @ints = (2, 1, 4, 2)
Output: true
For $i = 2, $j = 3
$ints[$i] = 4 => 2 * 2 =>  2 * $ints[$j]

Analysis

This is another one where ther is probably a one-liner, but I chose to write something a little more verbose;

First I create %exists such that $exists[$j] exists if $j occurs in @ints.

Then I simply loop through @ints checking whether
$exists{$j * 2} exists.

Note that since $i != $j is a requirement, I have to explicitly exclude the case where 0 appears in @ints.

Try it 

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2024-10-07
use utf8;     # Week 290 - task 1 - Double exist
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';

double_exist(6, 2, 3, 3);
double_exist(3, 1, 4, 13);
double_exist(2, 1, 4, 2);
double_exist(0, 0, 14, 7, -4, -8);

# bigger example
my @ints;
push @ints, int(rand(100)) for (0 .. 19);
double_exist(@ints);

sub double_exist {
    
    my (@ints, %exists, $explain, $j);
    
    # initialise
    @ints = @_;
    $exists{$_} = 1 for @ints;
    
    # find compliant pairs
    for $j (@ints) {
        $explain .= qq[$j and ] . ($j * 2) . ', ' if ($j != 0 and $exists{2 * $j});
    }
    
    # show results
    say qq[\nInput:  \@ints = (] . join(', ', @ints) . ')';
    say qq[Output: ] . ($explain ? (qq[true - ] . substr($explain, 0, -2)) : 'false');
}

Output

Input:  @ints = (6, 2, 3, 3)
Output: true - 3 and 6, 3 and 6

Input:  @ints = (3, 1, 4, 13)
Output: false

Input:  @ints = (2, 1, 4, 2)
Output: true - 2 and 4, 1 and 2, 2 and 4

Input:  @ints = (0, 0, 14, 7, -4, -8)
Output: true - 7 and 14, -4 and -8

Input:  @ints = (29, 87, 62, 35, 88, 66, 94, 60, 71, 79, 
   65, 96, 9, 4, 62, 62, 32, 39, 53, 9)
Output: false