Following script also does the job.Normally in Perl,array indexes starts from 0.

use strict;
use warnings;

my @my_arr = (
    [1,  11,  0,  0],
    [12, 109, 0,  0],
    [16, 1,   16, 0],
    [14, 14,  2,  0],
    [45, 16,  5,  4],
    );
my $index=$#my_arr;
while($index) {
push @diagonal,$my_arr[$index][$index-1];
--$index;
}
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print join '-', @diagonal;