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| -rwxr-xr-x | challenge-191/wlmb/perl/ch-2d.pl | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/challenge-191/wlmb/perl/ch-2d.pl b/challenge-191/wlmb/perl/ch-2d.pl new file mode 100755 index 0000000000..260fe94460 --- /dev/null +++ b/challenge-191/wlmb/perl/ch-2d.pl @@ -0,0 +1,55 @@ +#!/usr/bin/env perl +# Perl weekly challenge 191 +# Task 2: Cute List. Nested iterators. +# +# See https://wlmb.github.io/2022/11/14/PWC191/#task-2-cute-list +use v5.36; +use List::Util qw(all reduce); + +sub listit(@set){ # iterator that returns the elements of a set + sub { return shift @set } +} + +sub cute($n){ # return an iterator to generate all cute sequences of length $n + my @sets; + for my $position(0..$n-1){ + for(1..$n){ # Build sets of divisors and multiples of $position+1 + push @{$sets[$position]}, $_ if ($position+1)%$_==0 || $_%($position+1)==0; + } + } + sub aux{# closure for an ancilliary iterator constructor + sub ($pos) { # Returns an iterator for position $pos + #The iterator returns a cute subsecuence and a hash of seen values + # Return a trivial iterator if beyond end + return # trivial iterator beyond position + sub { state $n=0; return $n++? ():([],{})} if $pos >=@sets; + my @set=@{$sets[$pos]}; + my $it=aux($pos+1); # Iterator for next position + my $candidates=listit(@set); # iterator for candidates + my ($cute, $seen)=$it->(); # initial cute subsequence + sub { + while(1){ + while(my $candidate=$candidates->()){ + return([$candidate, @$cute], {$candidate, 1, %$seen}) + if !$seen->{$candidate}; + } + return () unless ($cute, $seen)=$it->(); # next subsequence or return + $candidates=listit(@set); # reinitalize iterator for candidates + } + } + } + } + aux(0); # return iterator for full sequence +} + +die << "EOF" unless @ARGV; +Usage: $0 N1 [N2...] +to count the cute orderings of 1..Ni +EOF +warn "Numbers beyond 20 will require patience" unless all {1<=$_<=18} @ARGV; +for(@ARGV){ + my $count=0; + my $it=cute($_); + ++$count while $it->(); # count cute sequences + say "$_-> $count"; # report +} |