diff options
| -rwxr-xr-x | challenge-141/jake/perl/ch-1.pl | 26 |
1 files changed, 16 insertions, 10 deletions
diff --git a/challenge-141/jake/perl/ch-1.pl b/challenge-141/jake/perl/ch-1.pl index 33fb88012c..93b65c6005 100755 --- a/challenge-141/jake/perl/ch-1.pl +++ b/challenge-141/jake/perl/ch-1.pl @@ -40,20 +40,24 @@ sub collect_numbers { # starting at 1 we aggregate all divisors in an array # we also aggregate all corresponding reciprocal values in another array +# these 2 lists contain all divisors: once ascending, once descending +# there's no need to check each number for modulo 0, we just need the first half of divisors +# we only need to find the middle of the lists before we have the entire list +# to do this we find the list element where both lists overlap, i.e. their symmetry axis # if these arrays are symmetric to each other at the position of half our's div_required, we know they have the required amount of divisors # example for even div_required = 8; num = 24; the divisor arrays are cross-symmetric at div_required / 2 # the axis is between $divisors[3] and $reciprocal[4] -# <==\\==> -# 24 12 8 6\\4 3 2 1 -# 1 2 3 4\\6 8 12 24 -# <==\\==> +# <==||==> +# 24 12 8 6||4 3 2 1 +# 1 2 3 4||6 8 12 24 +# <==||==> # # example for odd div_required = 9; num = 36; the divisor arrays are cross-symmetric at div_required / 2 # the axis is on $divisors[4] and $reciprocal[4] -# <==\ \==> -# 36 18 12 09 \06\ 04 03 02 01 -# 01 02 03 04 \06\ 09 12 18 36 -# <==\ \==> +# <==| |==> +# 36 18 12 09 |06| 04 03 02 01 +# 01 02 03 04 |06| 09 12 18 36 +# <==| |==> sub count_divisors { my ( $spec_num, $divisor) = @_; @@ -72,12 +76,14 @@ sub count_divisors { push @reciprocal, ( $num_atr->{num} / $divisor ); } - # if div_required is even we look for the axis between array elements + # if div_required is even we look for the axis BETWEEN array elements; see example above sub + # also we fist check if the values to be examined are actually defined to avoid unnecessary error messages if ( $num_atr->{div_required} % 2 == 0 ) { return $num_atr->{num} if $divisors[$num_atr->{div_required} / 2] && $divisors[$num_atr->{div_required} / 2] == $reciprocal[$num_atr->{div_required} / 2 - 1]; } - # if div_required is odd we look for the axis on an array element + # if div_required is odd we look for the axis ON an array element; see example above sub + # also we fist check if the values to be examined are actually defined to avoid unnecessary error messages if ( $num_atr->{div_required} % 2 == 1 ) { return $num_atr->{num} if $divisors[int($num_atr->{div_required} / 2)] && $divisors[int($num_atr->{div_required} / 2)] == $reciprocal[int($num_atr->{div_required} / 2)]; |