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#!/usr/bin/perl -s
use v5.16;
use Test2::V0;
use List::Util 'reductions';
use experimental 'signatures';
our $examples;
run_tests() if $examples; # does not return
die <<EOS unless @ARGV;
usage: $0 [-examples] [N...]
-examples
run the examples from the challenge
N...
Calculate the "triangular sum" over the given numbers.
EOS
### Input and Output
say triangular_sum(@ARGV);
### Implementation
sub triangular_sum (@n) {
# Calculate the running sums over the array starting with the second
# element until the array becomes a singleton.
@n = reductions {$a + $b} @n[1 .. $#n] while @n > 1;
$n[0];
}
### Examples and tests
sub run_tests {
# Meeting Slartibartfast, again.
is triangular_sum(1, 2, 3, 4, 5), 42, 'example 1';
is triangular_sum(1, 3, 5, 7, 9), 70, 'example 2';
done_testing;
exit;
}
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