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advent-of-code/2021/ruby/day_12.rb

26 lines
579 B

cave = Hash.new {|h,k| h[k] = [] }
ARGF.read.scan(/(\w+)-(\w+)/).each do
cave[_1] << _2
cave[_2] << _1
end
paths = [ %w[start] ]
loop do
closed, open = paths.partition { _1.last == "end" }
break if open.empty?
paths = closed + open.flat_map {|path|
cave.fetch(path.last)
# .reject { _1 =~ /^[a-z]+$/ && path.include?(_1) }
.reject { _1 == "start" }
.reject {|cave|
smalls = path.tally.select { _1 =~ /^[a-z]+$/ }
smalls.fetch(cave, 0) > (smalls.any? { _2 > 1 } ? 0 : 1)
}
.map { path + [_1] }
}
end
p paths.count