Range sum

You are given a list integers and pair of indices. Write a script to return the sum of the integers between the given indices (inclusive).

Examples

Example 1
Input: @ints = (-2, 0, 3, -5, 2, -1), $x = 0, $y = 2
Output: 1
Elements between indices (0, 2) => (-2, 0, 3)
Range Sum: (-2) + 0 + 3 => 1

Example 2
Input: @ints = (1, -2, 3, -4, 5), $x = 1, $y = 3
Output: -3
Elements between indices (1, 3) => (-2, 3, -4)
Range Sum: (-2) + 3 + (-4) => -3

Example 3
Input: @ints = (1, 0, 2, -1, 3), $x = 3, $y = 4
Output: 2
Elements between indices (3, 4) => (-1, 3)
Range Sum: (-1) + 3 => 2

Example 4
Input: @ints = (-5, 4, -3, 2, -1, 0), $x = 0, $y = 3
Output: -2
Elements between indices (0, 3) => (-5, 4, -3, 2)
Range Sum: (-5) + 4 + (-3) + 2 => -2

Example 5
Input: @ints = (-1, 0, 2, -3, -2, 1), $x = 0, $y = 2
Output: 1
Elements between indices (0, 2) => (-1, 0, 2)
Range Sum: (-1) + 0 + 2 => 1

Analysis

Perl's implementation of array slices reduces this task to:

$sum += $_ for @integers[$x .. $y];

In 'real life' one would check that $x and $y were within the bounds of the array and that $y >= $x, but as Perl gives an intelligible error message if those conditions occur I think I'll leave it at that.

Both solutions are written in readable, beginner-friendly style with comments and example calls.

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

I am sorry that the 'Try it' feature is currently working very slowly or not at all owing to some issue with my web hosting provider.

Try it 

Try running the script with any input:

Your @array =

example: 1, 2, 3, 4, 5

Your $x, $y =

example: 1, 3

⤡

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2025-08-11
use utf8;     # Week 334 - task 1 - Range sum
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';
use Encode;

range_sum([-2, 0, 3, -5, 2, -1], 0, 2);
range_sum([1, -2, 3, -4, 5], 1, 3);
range_sum([1, 0, 2, -1, 3], 3, 4);
range_sum([-5, 4, -3, 2, -1, 0], 0, 3);
range_sum([-1, 0, 2, -3, -2, 1], 0, 2);

sub range_sum {
    
    my (@integers, $from, $to, $sum);
    
    # do it
    @integers = @{$_[0]};
    $sum += $_ for @integers[$_[1] .. $_[2]];
    
    say qq[\nInput:  \@integers = (] . join(', ', @integers) . qq[), \$x = $_[1], \$y = $_[2]]; 
    say qq[Output: $sum];
}

6 lines of code

Output from script

Input:  @integers = (-2, 0, 3, -5, 2, -1), $x = 0, $y = 2
Output: 1

Input:  @integers = (1, -2, 3, -4, 5), $x = 1, $y = 3
Output: -3

Input:  @integers = (1, 0, 2, -1, 3), $x = 3, $y = 4
Output: 2

Input:  @integers = (-5, 4, -3, 2, -1, 0), $x = 0, $y = 3
Output: -2

Input:  @integers = (-1, 0, 2, -3, -2, 1), $x = 0, $y = 2
Output: 1