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32 lines
819 B
32 lines
819 B
3 years ago
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require "set"
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INPUT = ARGF.read.split("\n").map {|l| l.chars.map(&:to_i) }
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NEIGHBORS = [[0,-1], [-1, 0], [1, 0], [0, 1]]
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def neighbors(y,x)
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NEIGHBORS
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.map {|dy,dx| [y+dy, x+dx] }
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.select {|y,x| (0...INPUT.size).cover?(y) && (0...INPUT[0].size).cover?(x) }
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end
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all = (0...INPUT.size).flat_map {|y| (0...INPUT[0].size).map {|x| [y, x]}}
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lows = all.select {|y,x| neighbors(y,x).all? {|yy,xx| INPUT[yy][xx] > INPUT[y][x] }}
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# p lows.sum {|y,x| INPUT[y][x] + 1 }
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def fill_basin(low)
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basin = Set.new([low])
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stack = [low]
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until stack.empty?
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y,x = stack.shift
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new_neighbors = neighbors(y,x).reject {|y,x| basin.include?([y,x]) || INPUT[y][x] == 9 }
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stack.concat(new_neighbors)
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basin.merge(new_neighbors)
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end
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basin
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end
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p lows.map { fill_basin(_1) }.map(&:size).sort[-3, 3].inject(:*)
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