Question

I have a data that looks like this:

3
2
1
5

What I want to get is the “decreasing” cumulative of this data
yielding

11
8
6
5
0

What is the compact way of doing that in Perl?

Answer 1

perl -e '{ my @a = (3,2,1,5); map { $s+=$_ } @a; 
           map { print "$s\n"; $s-= $_ } (@a,0) }'

or

perl -e '{ my @a = (3,2,1,5); my @r = (0); 
           map { $s += $_ ; push @r, $s } reverse @a; 
           print join("\n", reverse @r)."\n" }'

Note: these both require an extra statement my $s=0; using strict.

But may I ask WHY?