TL;DR

Here we are with TASK #1 from The Weekly Challenge #238. Enjoy!

The challenge

You are given an array of integers.

Write a script to return the running sum of the given array. The running sum can be calculated as sum[i] = num[0] + num[1] + …. + num[i].

Example 1

Input: @int = (1, 2, 3, 4, 5)
Output: (1, 3, 6, 10, 15)

Example 2

Input: @int = (1, 1, 1, 1, 1)
Output: (1, 2, 3, 4, 5)

Example 3

Input: @int = (0, -1, 1, 2)
Output: (0, -1, 0, 2)

The questions

I’d probably just ask:

• the domain of the inputs (i.e. should we prepare for big integers?)
• the length of the input/output arrays.

The solution

We can iterate over the input array and collect stuff along the way, using an accumulator variable. Here’s how to do it in Raku:

#!/usr/bin/env raku
use v6;
sub MAIN (*@args) { say running-sum(@args) }

sub running-sum (@int) {
   my $accumulator = 0;
   return [ @int.map({$accumulator += $_}) ];
}

I didn’t really like the accumulator variable, so I tried to implement an alternative solution with gather/take:

sub running-sum-alternative (@int) {
   return [ gather { take @int[0]; @int.reduce({ take $^a + $^b }) } ]
}

Still not that satisfactory, though. Surely Raku has something to the point, right? Right, let’s produce!

sub running-sum-alternative2 (@int) { @int.produce(&[+]) }

Surely Perl has something too, right? Right, let’s use reductions!

#!/usr/bin/env perl
use v5.24;
use warnings;
use List::Util 'reductions';

say '(', join(', ', running_sum(@ARGV)), ')';

sub running_sum { reductions { $a + $b } @_ }

That’s all for this challenge, folks!