Advent of Code

2.rb

data = File.readlines('./input/2.txt').map(&:strip).map do |line|
  range, character, string = line.split /:? /
  [range.split('-').map(&:to_i), character, string]
end

# Part 1

valid = data.select do |range, character, string|
  string.count(character).between?(*range)
end

puts valid.length

# Part 2

valid = data.select do |indices, character, string|
  candidates = indices.map { |i| string[i-1] }
  candidates.include?(character) && candidates.uniq.length > 1
end

puts valid.length

3.rb

map = File.readlines('./input/3.txt').map(&:strip)

num_columns = map[0].length

# Part 1

column = 0
row = 0
trees = 0

while row < map.length - 1 do
  column += 3
  row += 1

  if column >= num_columns
    column = column - num_columns
  end

  trees += map[row][column] == '#' ? 1 : 0
end

puts trees

# Part 2

slopes = [
  [1, 1],
  [3, 1],
  [5, 1],
  [7, 1],
  [1, 2]
]

product = 1

slopes.each do |x, y|
  column = 0
  row = 0
  trees = 0

  while row < map.length - 1 do
    column += x
    row += y

    if column >= num_columns
      column = column - num_columns
    end

    trees += map[row][column] == '#' ? 1 : 0
  end

  product *= trees
end

puts product

4.rb

passports = File.read('./input/4.txt').strip.split(/\n\n/)
.map { |passport| passport.split(/\s/).map { |row| row.split(':') }.to_h }

# Part 1

valid = passports
.select { |passport| (passport.keys.sort - ['cid']) == %w[byr ecl eyr hcl hgt iyr pid] }

puts valid.length

# Part 2

valid = passports
.select { |passport| (passport.keys.sort - ['cid']) == %w[byr ecl eyr hcl hgt iyr pid] }
.select { |passport| passport['byr'] =~ /\A\d{4}\z/ && passport['byr'].to_i.between?(1920, 2002) }
.select { |passport| passport['iyr'] =~ /\A\d{4}\z/ && passport['iyr'].to_i.between?(2010, 2020) }
.select { |passport| passport['eyr'] =~ /\A\d{4}\z/ && passport['eyr'].to_i.between?(2020, 2030) }
.select { |passport| passport['hcl'] =~ /\A#[0-9a-f]{6}\z/ }
.select { |passport| passport['ecl'] =~ /\A(amb|blu|brn|gry|grn|hzl|oth)\z/ }
.select { |passport| passport['pid'] =~ /\A\d{9}\z/ }
.select { |passport| passport['hgt'] =~ /\A\d+(cm|in)\z/ }
.select do |passport|
  if passport['hgt'] =~ /cm/
    passport['hgt'][/\d+/].to_i.between?(150, 193)
  else
    passport['hgt'][/\d+/].to_i.between?(59, 76)
  end
end

puts valid.length