Task

Find and display the sum of elements that are below the main diagonal of a matrix.

The matrix should be a square matrix.



 ───   Matrix to be used:   ───


     [[1,3,7,8,10],
      [2,4,16,14,4],
      [3,1,9,18,11],
      [12,14,17,18,20],
      [7,1,3,9,5]] 



#!/usr/bin/perl
 
use strict;
use warnings;
use List::Util qw( sum );
 
my $matrix =
  [[1,3,7,8,10],
  [2,4,16,14,4],
  [3,1,9,18,11],
  [12,14,17,18,20],
  [7,1,3,9,5]];
 
my $lowersum = sum map @{ $matrix->[$_] }[0 .. $_ - 1], 1 .. $#$matrix;
print "lower sum = $lowersum\n";