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50 lines
1.2 KiB
50 lines
1.2 KiB
class HeightMap
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NEIGHBORS = [[0, -1], [-1, 0], [0, 1], [1, 0]]
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def initialize(heights)
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@heights = heights
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end
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def shortest(from:, to:, &cond)
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frontier = [from]
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visited = { from => 0 }
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until frontier.empty? || to.any? { visited.has_key?(_1) }
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current = frontier.shift
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NEIGHBORS.each do |delta|
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candidate = current.zip(delta).map { _1 + _2 }
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next if visited.has_key?(candidate)
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next unless cand_height = @heights[candidate]
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next unless cond.(@heights.fetch(current), cand_height)
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visited[candidate] = visited.fetch(current) + 1
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frontier << candidate
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end
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frontier.sort_by { visited.fetch(_1) }
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end
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visited.find {|k,v| to.include?(k) }.last
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end
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end
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heights = ARGF.read.lines(chomp: true).map(&:chars)
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.flat_map.with_index {|row,y|
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row.map.with_index {|height,x| [[y, x], height] }
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}.to_h
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s, e = heights.invert.values_at(?S, ?E)
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heights[s] = ?a
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heights[e] = ?z
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hm = HeightMap.new(heights)
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# part one
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p hm.shortest(from: s, to: [e]) { _1.ord + 1 >= _2.ord }
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# part two
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as = heights.select { _2 == ?a }.map(&:first)
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p hm.shortest(from: e, to: as) { _1.ord - 1 <= _2.ord }
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