lanternfish

day6.rb

# day 6

test_input = [3, 4, 3, 1, 2]

input = test_input # set puzzle input here
@lantern_fish = Hash.new(0)

0.upto(input.max) do |counts|
  @lantern_fish[counts] = input.count(counts)
end

## start hatching

def pass_day(days: 1)
  days.times do
    hatch_count = @lantern_fish[0] # how many lanternfish are going to hatch after the day passes

    0.upto(@lantern_fish.keys.max).with_index do |index|
      @lantern_fish[index] = @lantern_fish[index + 1] if index !=8
    end

    @lantern_fish[8] = hatch_count
    @lantern_fish[6] += hatch_count #hatch count is the same as 'reset to 6' count
  end
end

pass_day(days: 80); @lantern_fish.values.sum # part 1 solution
pass_day(days: 176); @lantern_fish.values.sum # part 2 solution (days: 256 if starting from new data)