63 lines
1 KiB
Ruby
63 lines
1 KiB
Ruby
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require "set"
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$headX = 0
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$headY = 0
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$tailX = 0
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$tailY = 0
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$tailPositions = Set[[$tailX, $tailY]]
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def moveStep(dx, dy)
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$headX += dx
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$headY += dy
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dx = $headX - $tailX
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dy = $headY - $tailY
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case [dx.abs, dy.abs]
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when [0, 0], [1, 1], [1, 0], [0, 1] then
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when [2, 0], [0, 2], [2, 2] then
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$tailX += dx <=> 0
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$tailY += dy <=> 0
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when [2, 1] then
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$tailX += dx <=> 0
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$tailY += dy <=> 0
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when [1, 2] then
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$tailX += dx <=> 0
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$tailY += dy <=> 0
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else
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puts "Unknown: (#{dx}, #{dy})"
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raise
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end
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$tailPositions.add [$tailX, $tailY]
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end
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for line in File.readlines('day9.input')
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unless /^(?<dir>[RLUD]) (?<steps>\d+)$/ =~ line
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puts "Failed to parse #{line}"
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raise
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end
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steps = steps.to_i
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case dir
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when "R" then
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steps.times { moveStep 1, 0 }
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when "L" then
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steps.times { moveStep -1, 0 }
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when "U" then
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steps.times { moveStep 0, 1 }
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when "D" then
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steps.times { moveStep 0, -1 }
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else
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raise
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end
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end
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puts $tailPositions.count
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