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74 lines
1.1 KiB
74 lines
1.1 KiB
input = DATA.readlines(chomp: true)
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.flat_map.with_index {|line, j|
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line.chars.map.with_index {|x, i|
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[[j,i], x]
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}
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}.to_h
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TURNS = {
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[-1,0] => [0,1],
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[0,1] => [1,0],
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[1,0] => [0,-1],
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[0,-1] => [-1,0],
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}
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Loop = Class.new(Exception)
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def patrol(lab)
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start = lab.find { _2 == ?^ }.first
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path = [[start, [-1,0]]]
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seen = path.to_set
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loop do
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pos, dir = path.last
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peek = pos.zip(dir).map {|i,di| i + di }
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return path unless lab.has_key?(peek)
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raise Loop if seen.include?([peek, dir])
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seen << [peek, dir]
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case lab.fetch(peek)
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when ?., ?^
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path << [peek, dir]
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when ?#
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path.last[1] = TURNS.fetch(dir)
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when nil
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return path
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else
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fail
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end
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end
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end
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def loop?(lab)
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patrol(lab)
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false
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rescue Loop
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true
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end
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path = patrol(input).map(&:first).to_set
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pp path.length
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pp input
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.select { path.include?(_1) && _2 != ?^ }
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.select {|xy, _|
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# pp xy
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input[xy] = ?#
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res = loop?(input)
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input[xy] = ?.
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res
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}.size
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__END__
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....#.....
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.........#
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..........
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..#.......
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.......#..
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..........
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.#..^.....
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........#.
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#.........
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......#...
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