Advent of Code, Day 20

day20_part1.rb

#!/usr/bin/env ruby

# http://adventofcode.com/day/20

input = 34000000

def deliver_presents(num_houses)   
  presents = [0] + [0] * num_houses
  (1..num_houses).each do |elf|
    (elf..num_houses).step(elf) do |house_number|
      presents[house_number] += 10 * elf
    end
  end
  presents
end

num_houses = 1
presents = nil
loop do
  presents = deliver_presents(num_houses)
  max_presents = presents.max
  break if max_presents >= input
  num_houses *= 10
end
i = presents.index do |p|
  p >= input
end
puts i

day20_part2.rb

#!/usr/bin/env ruby

# http://adventofcode.com/day/20

input = 34000000

def deliver_presents(num_houses)
  presents = [0] + [0] * num_houses
  (1..num_houses).each do |elf|
    visits = 0
    (elf..num_houses).step(elf) do |house_number|
      presents[house_number] += 11 * elf
      visits += 1
      break if visits == 50
    end
  end
  presents
end

num_houses = 1
presents = nil
loop do
  presents = deliver_presents(num_houses)
  max_presents = presents.max
  break if max_presents >= input
  num_houses *= 10
end
i = presents.index do |p|
  p >= input
end
puts i