#!/usr/bin/env ruby

require "debug"

problem = 10
@input = File.readlines("#{problem}.input")
#@input = DATA.read.split("\n")
  .map { _1.strip.chars.map { |c| c == "." ? "." : c.to_i }}
@debug = @input.size < 20
#@debug = true

def bounded?(point)
  point.first >= 0 &&
    point.last >= 0 &&
    point.first < @input.size &&
    point.last < @input.first.size
end

def traverse(start, height = 1)
  result = [
    [start.first - 1, start.last],
    [start.first + 1, start.last],
    [start.first, start.last - 1],
    [start.first, start.last + 1]
  ].map do |point|
    if !bounded?(point) || @input.dig(*point) == "."
      []
    elsif @input.dig(*point) == 9 && height == 9
      if @debug
        @paths[point.first][point.last] = @input.dig(*point)
      end
      [point]
    elsif @input.dig(*point) == height
      traverse(point, height + 1).flatten(1)
    else # if @input.dig(*point) != height
      []
    end
  end

  if result.size > 0 && @debug
    @paths[start.first][start.last] = @input.dig(*start)
  end

  result
end

if @debug
  @paths = Array.new(@input.size) { Array.new(@input.first.size) { "." } }
end

result = (0...@input.size).flat_map do |x|
  (0...@input.first.size).map do |y|
    [[x, y], traverse([x, y]).flatten(1)] if @input[x][y] == 0
  end.compact
end.to_h

if @debug
  puts @paths.map(&:join).join("\n")
end

p result.values.map { _1.uniq.size }.sum
p result.values.map { _1.size }.sum

__END__
89010123
78121874
87430965
96549874
45678903
32019012
01329801
10456732