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require "forwardable"
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DIR_DELTAS = {
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N: [-1, 0],
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W: [ 0, -1],
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E: [ 0, 1],
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S: [ 1, 0],
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}
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TILE_NEIGHBOR_DELTAS = {
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?| => "NS",
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?- => "EW",
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?L => "NE",
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?J => "NW",
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?7 => "SW",
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?F => "SE",
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?S => "NEWS",
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}.transform_values {|dirs| dirs.chars.map { DIR_DELTAS.fetch(_1.to_sym) }}
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Tiles = Data.define(:tiles) do
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extend Forwardable
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def_delegator :tiles, :key
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def_delegator :tiles, :fetch
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def_delegator :tiles, :size
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def neighbors(coord)
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TILE_NEIGHBOR_DELTAS.fetch(self.fetch(coord))
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.map {|delta| coord.zip(delta).map { _1 + _2 }}
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.select { tiles.has_key?(_1) }
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end
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def to_s
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coords = tiles.keys
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y_range, x_range = *extents
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y_range.map {|y|
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x_range.map {|x| tiles.fetch([y,x], ?.) }.join
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}.join("\n")
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end
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def extents
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y_range = Range.new(*tiles.keys.map(&:first).minmax)
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x_range = Range.new(*tiles.keys.map(&:last).minmax)
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[y_range, x_range]
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end
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end
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tiles = ARGF.readlines(chomp: true).each.with_index.inject({}) {|tiles, (row, y)|
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tiles.merge(
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row.chars.each.with_index
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.reject {|tile,_| tile == ?. }
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.to_h {|tile,x| [[y,x], tile] }
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)
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}
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tiles = Tiles.new(tiles)
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start = tiles.key(?S)
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seed = tiles.neighbors(start)
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.find {|candidate|
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tiles.neighbors(candidate).any? { tiles.fetch(_1) == ?S }
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}
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loop_ = [seed]
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until loop_.last == start
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cur = loop_.last
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loop_ << tiles.neighbors(cur)
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.reject { _1 == loop_[-2] }
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.first
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end
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# fix the start tile
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start_dirs = [seed, loop_[-2]].map {|coord| start.zip(coord).map { _2 - _1 }}
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tile = TILE_NEIGHBOR_DELTAS.find { _2.sort == start_dirs.sort }[0]
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tiles.tiles[start] = tile
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loop_ = Tiles.new(loop_.to_h { [_1, tiles.fetch(_1)] })
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# puts loop_
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# part one
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p loop_.size / 2
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# part two
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y_range, x_range = *loop_.extents
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p y_range.sum {|y|
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x_range.chunk_while {|x_a, x_b|
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a = loop_.fetch([y, x_a], nil)
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b = loop_.fetch([y, x_b], nil)
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# it's a chunk if it's multiple empty tiles or a pipe that goes east
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(a.nil? && b.nil?) || (a && TILE_NEIGHBOR_DELTAS.fetch(a).include?([0,1]))
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}.select {|chunk|
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# keep empty tiles
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end_tiles = chunk.values_at(0, -1).map {|x| loop_.fetch([y,x], nil) }
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next true if end_tiles.all?(&:nil?)
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# only keep pipes that cross the horizontal axis
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deltas = end_tiles.flat_map {|tile| TILE_NEIGHBOR_DELTAS.fetch(tile) }
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[[-1,0], [1,0]].all? {|dy| deltas.include?(dy) }
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}.sum {|chunk|
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tiles = chunk.map {|x| loop_.fetch([y,x], nil) }
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(tiles[0]...tiles[0]) ? tiles.count(nil) : 0 # lol
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}
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}
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