AdventOfCode 2021 Day 3

3.rb

# https://adventofcode.com/2021/day/3

require 'pp'
require_relative 'get_response'

# Abstracted getting/parsing input
raw = GetResponse.new(day: 3).call

# ----- Part 2 ------
# writing my own transpose just for fun
def transpose(raw)
  transposed = Array.new(raw.first.length) { Array.new(raw.length) }

  raw.each.with_index do |row, i|
    row.split("").each.with_index do |cell, j|
      transposed[j][i] = cell
    end
  end

  transposed
end

transposed = transpose(raw)

gamma = raw.length.times.map { |i| i }
epsilon = raw.length.times.map { |i| i }

def reduce(row, indices, mode:)
  return indices if indices.length <= 1

  one = 0
  zero = 0

  indices.each do |idx|
    row[idx] == "1" ? (one += 1) : (zero += 1)
  end

  indices.map do |idx|
    target = if mode == :gamma
      one >= zero ? "1" : "0"
    else
      zero <= one ? "0" : "1"
    end
    row[idx] == target ? idx : nil
  end.compact
end

transposed.each.with_index do |row, i|
  gamma = reduce(row, gamma, mode: :gamma)
  epsilon = reduce(row, epsilon, mode: :epsilon)
end

ox = raw[gamma.first].to_i(2)
co2 = raw[epsilon.first].to_i(2)

pp ox * co2

# ------ Pt. 1 --------
# buckets, gamma, epsilon = 3.times.map { Array.new(12) { 0 } }
# pp [buckets, gamma, epsilon]

# raw.each do |row|
#   row.split("").each.with_index do |digit, i|
#     buckets[i] += (digit == "1" ? 1 : -1)
#   end
# end

# buckets.each.with_index do |digit, i|
#   if digit > 0
#     gamma[i] = "1"
#     epsilon[i] = "0"
#   else
#     gamma[i] = "0"
#     epsilon[i] = "1"
#   end
# end

# pp [ gamma, epsilon ]