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45 lines
938 B
45 lines
938 B
require "set"
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motions = ARGF.read.scan(/([RLUD])\s+(\d+)/).map { [_1, _2.to_i] }
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class Snake
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def initialize
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@knots = Array.new(10) { [0, 0] }
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end
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def tail = @knots.last
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def move!(dir)
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delta = case dir
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when ?L then [ 0, -1]
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when ?U then [ 1, 0]
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when ?R then [ 0, 1]
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when ?D then [-1, 0]
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else fail dir.inspect
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end
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@knots[0] = @knots[0].zip(delta).map { _1 + _2 }
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@knots = @knots[1..].inject([@knots[0]]) {|knots, tail|
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head = knots.last
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delta = head.zip(tail).map { _1 - _2 }
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knots << if delta.any? { _1.abs > 1 }
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tail.zip(delta.map { _1.clamp(-1, 1) }).map { _1 + _2 }
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else
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tail
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end
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}
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end
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end
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snake = Snake.new
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seen = Set.new
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motions.each do |dir, distance|
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distance.times do
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snake.move!(dir)
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seen << snake.tail
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end
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end
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p seen.size
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