my $arr  = ['A -4 C',
            'C -4 B',
            'B -4 A',
            'A -2 C',
            'C -3 B'];

my @res = decomp_a2aoa_wth_idx($arr);

sub decomp_a2aoa_wth_idx
{
    my  $arr    = shift;
    return map { [ split (" ",$arr->[$_],$_) ] } (0 .. @{$arr}-1);
}

__END__
# Prints this result
$VAR1 = [
          ['A','-4','C'],
          ['C -4 B'],
          ['B','-4 A'],
          ['A','-2','C'],
          ['C','-3','B']
];