day08.rb

if ARGV.empty?
  data = DATA.readlines
else
  data = File.readlines(ARGV[0])
end

trees = data
  .map(&:chomp)
  .map {_1.chars}
  .map {_1.map(&:to_i)}

def check_visible(trees, i, j)
  height = trees[i][j]
  row = trees[i]
  col = trees.transpose[j]

  return 1 if i == 0 || j == 0 || i == trees.length - 1 || j == trees.first.length - 1
  return 1 if height > row[0...j].max
  return 1 if height > row[j+1..-1].max
  return 1 if height > col[0...i].max
  return 1 if height > col[i+1..-1].max

  0
end

def visibility(trees)
  trees.length.times.flat_map do |i|
    trees.first.length.times.map do |j|
      check_visible(trees, i, j)
      # Part 2
      # scenic_score(trees, i, j)
    end
  end
end

def scenic_score(trees, i, j)
  height = trees[i][j]
  row = trees[i]
  col = trees.transpose[j]
  scores = []

  # To the left
  score = 0
  (j-1).downto(0).each do |k|
    score += 1
    break if row[k] >= height
  end
  scores << score

  # To the right
  score = 0
  (j+1...trees.first.length).each do |k|
    score += 1
    break if row[k] >= height
  end
  scores << score

  # Above
  score = 0
  (i-1).downto(0).each do |k|
    score += 1
    break if col[k] >= height
  end
  scores << score

  # Below
  score = 0
  (i+1...trees.length).each do |k|
    score += 1
    break if col[k] >= height
  end
  scores << score

  scores.inject(:*)
end

if ARGV.empty?
  require 'rspec/autorun'
  RSpec.describe 'day08' do
    it 'works for the example case' do
      expect(visibility(trees)).to eq([
        [1, 1, 1, 1, 1],
        [1, 1, 1, 0, 1],
        [1, 1, 0, 1, 1],
        [1, 0, 1, 0, 1],
        [1, 1, 1, 1, 1],
      ].flatten)
    end

    it 'works on the scenic stuff' do
      expect(scenic_score(trees, 1, 2)).to eq(4)
      expect(scenic_score(trees, 3, 2)).to eq(8)
    end
  end
end

p visibility(trees)


__END__
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https://youtu.be/3SHQOyUVvgA