11.rb

#!/usr/bin/env ruby

require 'pp'

#FILENAME = 'input.txt'
FILENAME = 'input_small.txt'

#stars = []
#File.readlines(FILENAME).each do |line|
#  posx, posy, velx, vely = line
#    .match(/position=<\s*(-?\d+),\s*(-?\d+)> velocity=<\s*(-?\d+),\s*(-?\d+)>/i)
#    .captures.map{ |x| x.to_i }
#  star = {posx: posx, posy: posy, velx: velx, vely: vely}
#  stars.push(star)
#end

class Grid
  def self.calc(x, y, serial)
    @grid_calculations ||=
      Hash.new do |h, key|
        x = key[0]
        y = key[1]
        serial = key[2]
        rack_id = x + 10
        power = ((rack_id * y) + serial) * rack_id
        hundreds = ((power / 100) % 10).floor
        h[key] = hundreds - 5
      end
    @grid_calculations[[x, y, serial]]
  end
end

raise 'fail1' unless Grid.calc(3, 5, 8) == 4
raise 'fail2' unless Grid.calc(122, 79, 57) == -5
raise 'fail3' unless Grid.calc(217, 196, 39) == 0
raise 'fail4' unless Grid.calc(101, 153, 71) == 4
raise 'fail5' unless Grid.calc(3, 5, 8) == 4
raise 'fail6' unless Grid.calc(122, 79, 57) == -5
raise 'fail7' unless Grid.calc(217, 196, 39) == 0
raise 'fail8' unless Grid.calc(101, 153, 71) == 4
puts 'Passed tests'

puts 'Part 1'
max_val = 0
max_x = -1
max_y = -1
serial = 1_308

(1).upto(300 - 3) do |y|
  (1).upto(300 - 3) do |x|
    val = 0
    (0).upto(2) do |yadd|
      (0).upto(2) { |xadd| val += Grid.calc(x + xadd, y + yadd, serial) }
    end
    if (max_val < val)
      max_val = val
      max_x = x
      max_y = y
      puts "New Max #{max_val} (#{max_x}, #{max_y})"
    end
  end
end

puts 'Part 2'
max_val = 0
max_x = -1
max_y = -1
serial = 1_308
#size = 3

(1).upto(300) do |size|
  (1).upto(300 - size) do |y|
    (1).upto(300 - size) do |x|
      val = 0
      (0).upto(size - 1) do |yadd|
        (0).upto(size - 1) do |xadd|
          val += Grid.calc(x + xadd, y + yadd, serial)
        end
      end
      if (max_val < val)
        max_val = val
        max_x = x
        max_y = y
        max_size = size
        puts "New Max #{max_val} (#{max_x}, #{max_y}, #{size})"
      end
    end
  end
end

## Failed Guesses
# 235,86,13