Task — Zero friend

You are given a list of numbers. Find the number that is closest to zero and return its distance to zero.

Examples

Example 1
Input: @nums = (4, 2, -1, 3, -2)
Output: 1
Values closest to 0: -1 and 2 (distance = 1 and 2)

Example 2
Input: @nums = (-5, 5, -3, 3, -1, 1)
Output: 1
Values closest to 0: -1 and 1 (distance = 1)

Example 3
Input: @ums = (7, -3, 0, 2, -8)
Output: 0
Values closest to 0: 0 (distance = 0)
Exact zero wins regardless of other close values.

Example 4
Input: @nums = (-2, -5, -1, -8)
Output: 1
Values closest to 0: -1 and -2 (distance = 1 and 2)

Example 5
Input: @nums = (-2, 2, -4, 4, -1, 1)
Output: 1
Values closest to 0: -1 and 1 (distance = 1)

Analysis

As is often the case, there is a choice between a concise solution and the most efficient one. I've gone for conciseness this time.

My solution is to sort the given array by absolute value, for which Perl conveniently provides:

my @x = sort {abs($a) <=> abs($b)} @_;

The answer is then simply abs($x[0]).

Perl has an efficient sort operation, so this is pretty fast even for a long array: I tried 1000 numbers and it completed in under a second. However, for a very long array it would probably be quicker to do a single pass along the array, comparing the absolute value of each element against the smallest seen so far.

I noted that the array was stated to be of 'numbers' rather than integers, and you will see from my tests that it also works for floating point numbers.

Try it 

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2025-10-13
use utf8;     # Week 343 - task 1 - Zero friend
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';
use Encode;

zero_friend(4, 2, -1, 3, -2);
zero_friend(-5, 5, -3, 3, -1, 1);
zero_friend(7, -3, 0, 2, -8);
zero_friend(71.6, -93.4, 102.102, -1000, 41.2, -70.9, 999, 4e6, -1e-3);

# bigger example
my @ints;
push @ints, (int(rand(1e6) - 5e5)) / 1e3 for 0 .. 49;
zero_friend(@ints);

sub zero_friend {
    
    # sort by absolute values
    my @x = sort {abs($a) <=> abs($b)} @_;
    
    say qq[\nInput:  ] . join(', ', @_);
    say qq[Output: ] . abs($x[0]);
}

Output

Input:  4, 2, -1, 3, -2
Output: 1

Input:  -5, 5, -3, 3, -1, 1
Output: 1

Input:  7, -3, 0, 2, -8
Output: 0

Input:  71.6, -93.4, 102.102, -1000, 41.2, -70.9, 999,
   4000000, -0.001
Output: 0.001

Input:  -478.251, 211.44, 382.593, 23.986, 175.974,
   120.869, 77.025, 452.896, -138.822, -127.616, -199.365,
   169.603, 216.2, -294.691, -479.728, 491.744, -325.153,
   -214.099, -377.572, 61.443, -492.841, -273.27,
   -349.304, 115.779, 425.666, 127.48, -363.688, 452.505,
   454.606, 301.836, -289.928, 404.138, -107.246, 155.597,
   192.101, 412.444, 466.311, 460.197, -377.281, 481.047,
   -281.096, 165.08, -342.416, -255.452, 451.143,
   -431.013, -458.835, 136.978, -439.602, 47.112
Output: 23.986