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94 lines
2.0 KiB
94 lines
2.0 KiB
12 months ago
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require "set"
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walls = Set.new
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blizzards = Hash.new {|h,k| h[k] = Set.new }
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clear_ground = Set.new
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ARGF.read.lines(chomp: true).each.with_index do |row, y|
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row.chars.each.with_index do |pos,x|
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case pos
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when ?#
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walls.add([y,x])
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when /[v^<>]/
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blizzards[pos].add([y,x])
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when ?.
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clear_ground.add([y,x])
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else
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fail pos
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end
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end
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end
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x_range = Range.new(*walls.map(&:last).minmax)
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y_range = Range.new(*walls.map(&:first).minmax)
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debug = ->() do
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puts
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puts y_range.map {|y|
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x_range.map {|x|
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if walls.include?([y,x])
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?#
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elsif blizzards.any? {|_,pos| pos.include?([y,x])}
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b = blizzards.select {|_,pos| pos.include?([y,x])}
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(b.size == 1) ? b.keys[0] : b.size
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else
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?.
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end
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}.join
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}.join("\n")
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end
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start = [0, clear_ground.find {|y,x| y == 0 }.last]
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goal = [y_range.end, clear_ground.find {|y,x| y == y_range.end }.last]
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dir_deltas = {
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?^ => [-1, 0],
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?v => [ 1, 0],
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?< => [ 0, -1],
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?> => [ 0, 1],
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}
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moves = [*dir_deltas.values, [0, 0]]
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frontier = [start]
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(1..).each do |time|
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if (time % 1).zero?
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puts time
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# p frontier
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# debug.()
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end
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blizzards = blizzards.to_h {|dir,positions|
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delta = dir_deltas.fetch(dir)
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edges, positions = positions
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.map {|pos| pos.zip(delta).map { _1 + _2 }}
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.partition { walls.include?(_1) }
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positions.concat(edges.map {|(y,x)|
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case dir
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when ?^ then [y_range.end - 1, x]
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when ?v then [y_range.begin + 1, x]
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when ?< then [y, x_range.end - 1]
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when ?> then [y, x_range.end + 1]
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else fail dir
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end
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})
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[dir, positions]
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}
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clear_ground = y_range.map {|y| x_range.map {|x| [y, x] }}.flatten(1)
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.reject {|pos| walls.include?(pos) || blizzards.any? { _2.include?(pos) }}
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options = frontier.map {|current|
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moves.filter_map {|delta|
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pos = current.zip(delta).map { _1 + _2 }
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clear_ground.include?(pos) && pos
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}
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}.flatten(1)
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frontier = options.uniq
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if frontier.include?(goal)
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puts time + 1
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exit
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end
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end
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