my $i = 0;
my @sorted_indicies = map { $_->[1] } 
                      sort { $a->[0] <=> $b->[0] }
                      map { [ $_, $i++ ] } @array;
# OR 
my @sorted_indicies = map { $_->[1] } 
                      sort { $a->[0] <=> $b->[0] }
                      map { [ $array[$_], $_ ] } (0..$#array);