5.rb

def parse_instructions(stack_instructions)
  stack_numbers = stack_instructions.last
  stacks = stack_numbers.scan(/\d/).map { [] }
  stack_instructions[0...-1].each do |row|
    stacks.each.with_index do |stack, index|
      crate = row[stack_numbers.index((index + 1).to_s)]
      stack << crate unless crate.strip.empty?
    end
  end
  stacks.map(&:compact)
end

stack_instructions, move_instructions = DATA.read.split("\n\n").map(&:lines)
# A
stacks = parse_instructions(stack_instructions)
move_instructions.each do |instruction|
  num, from, to = instruction.scan(/\d+/).map(&:to_i)
  num.times do
    crate = stacks[from - 1].shift(1)
    stacks[to - 1].unshift(crate).flatten!
  end
end

p "#a: #{stacks.map(&:first).join}"

# B
stacks = parse_instructions(stack_instructions)
move_instructions.each do |instruction|
  num, from, to = instruction.scan(/\d+/).map(&:to_i)
  crates = stacks[from - 1].shift(num)
  stacks[to - 1].unshift(crates).flatten!
end

p "#b: #{stacks.map(&:first).join}"
__END__
    [C]             [L]         [T]
    [V] [R] [M]     [T]         [B]
    [F] [G] [H] [Q] [Q]         [H]
    [W] [L] [P] [V] [M] [V]     [F]
    [P] [C] [W] [S] [Z] [B] [S] [P]
[G] [R] [M] [B] [F] [J] [S] [Z] [D]
[J] [L] [P] [F] [C] [H] [F] [J] [C]
[Z] [Q] [F] [L] [G] [W] [H] [F] [M]
 1   2   3   4   5   6   7   8   9 

move 1 from 5 to 6
move 5 from 6 to 7
move 10 from 7 to 3
move 4 from 8 to 4
move 2 from 5 to 4
move 4 from 3 to 6
move 6 from 2 to 4
move 8 from 6 to 9
move 5 from 9 to 2
move 7 from 2 to 7
move 2 from 1 to 4
move 3 from 3 to 8
move 1 from 5 to 9
move 1 from 3 to 8
move 1 from 1 to 2
move 11 from 4 to 6
move 2 from 5 to 6
move 10 from 9 to 1
move 4 from 8 to 3
move 7 from 7 to 1
move 9 from 1 to 2
move 1 from 6 to 5
move 1 from 5 to 9
move 5 from 3 to 8
move 2 from 9 to 1
move 5 from 3 to 9
move 3 from 6 to 8
move 5 from 9 to 6
move 6 from 6 to 3
move 3 from 3 to 2
move 1 from 9 to 8
move 13 from 2 to 3
move 3 from 8 to 1
move 11 from 1 to 4
move 3 from 4 to 1
move 2 from 6 to 5
move 4 from 6 to 8
move 17 from 3 to 9
move 1 from 1 to 8
move 1 from 6 to 5
move 1 from 3 to 7
move 1 from 7 to 4
move 3 from 4 to 1
move 1 from 3 to 8
move 4 from 8 to 1
move 3 from 5 to 9
move 1 from 6 to 4
move 4 from 4 to 8
move 2 from 8 to 4
move 2 from 1 to 6
move 4 from 8 to 6
move 1 from 8 to 3
move 6 from 6 to 3
move 6 from 3 to 9
move 6 from 1 to 4
move 5 from 8 to 4
move 1 from 3 to 6
move 3 from 1 to 7
move 1 from 6 to 7
move 4 from 4 to 5
move 24 from 9 to 5
move 2 from 9 to 1
move 27 from 5 to 7
move 13 from 7 to 2
move 1 from 5 to 9
move 7 from 2 to 7
move 1 from 9 to 8
move 5 from 2 to 8
move 1 from 2 to 5
move 1 from 5 to 7
move 21 from 4 to 1
move 1 from 4 to 6
move 1 from 6 to 5
move 22 from 7 to 5
move 2 from 7 to 8
move 7 from 5 to 4
move 1 from 4 to 5
move 2 from 7 to 9
move 5 from 5 to 2
move 5 from 4 to 2
move 3 from 5 to 1
move 7 from 8 to 7
move 1 from 4 to 1
move 23 from 1 to 8
move 2 from 9 to 4
move 11 from 8 to 3
move 3 from 1 to 3
move 1 from 4 to 2
move 12 from 3 to 2
move 7 from 7 to 3
move 3 from 2 to 1
move 1 from 4 to 9
move 1 from 1 to 3
move 9 from 8 to 6
move 2 from 5 to 4
move 3 from 1 to 7
move 3 from 2 to 4
move 7 from 2 to 3
move 9 from 3 to 4
move 7 from 5 to 2
move 2 from 7 to 2
move 1 from 7 to 2
move 13 from 4 to 6
move 1 from 9 to 8
move 2 from 8 to 2
move 12 from 2 to 1
move 3 from 3 to 1
move 1 from 8 to 1
move 5 from 3 to 7
move 3 from 2 to 8
move 7 from 2 to 5
move 3 from 8 to 3
move 1 from 4 to 8
move 22 from 6 to 4
move 1 from 3 to 6
move 3 from 5 to 8
move 4 from 5 to 8
move 1 from 3 to 9
move 8 from 4 to 2
move 8 from 8 to 3
move 1 from 6 to 3
move 4 from 2 to 6
move 1 from 9 to 4
move 5 from 3 to 9
move 2 from 8 to 1
move 3 from 2 to 1
move 10 from 4 to 8
move 4 from 7 to 6
move 10 from 1 to 3
move 9 from 8 to 2
move 1 from 7 to 1
move 15 from 3 to 1
move 1 from 8 to 9
move 4 from 4 to 1
move 17 from 1 to 3
move 3 from 2 to 3
move 3 from 6 to 8
move 5 from 9 to 7
move 11 from 1 to 8
move 4 from 7 to 8
move 6 from 2 to 5
move 2 from 1 to 4
move 4 from 6 to 8
move 16 from 8 to 6
move 2 from 6 to 1
move 1 from 9 to 5
move 1 from 7 to 5
move 2 from 5 to 6
move 5 from 6 to 3
move 2 from 8 to 5
move 1 from 2 to 1
move 10 from 6 to 3
move 6 from 5 to 9
move 2 from 1 to 2
move 2 from 4 to 2
move 1 from 2 to 4
move 5 from 9 to 2
move 1 from 4 to 3
move 1 from 9 to 7
move 1 from 6 to 1
move 1 from 1 to 7
move 2 from 7 to 5
move 7 from 2 to 5
move 6 from 5 to 1
move 1 from 2 to 3
move 1 from 4 to 1
move 2 from 8 to 9
move 8 from 1 to 3
move 2 from 5 to 3
move 29 from 3 to 9
move 5 from 3 to 8
move 6 from 8 to 5
move 1 from 6 to 5
move 6 from 3 to 2
move 2 from 2 to 4
move 1 from 1 to 7
move 18 from 9 to 6
move 2 from 2 to 9
move 2 from 2 to 8
move 13 from 6 to 8
move 1 from 7 to 4
move 3 from 5 to 6
move 1 from 5 to 7
move 1 from 7 to 4
move 14 from 9 to 3
move 3 from 4 to 5
move 1 from 9 to 7
move 14 from 3 to 2
move 1 from 7 to 3
move 4 from 2 to 5
move 16 from 8 to 6
move 11 from 6 to 9
move 13 from 6 to 4
move 5 from 5 to 2
move 12 from 2 to 4
move 19 from 4 to 3
move 7 from 4 to 5
move 14 from 5 to 2
move 2 from 3 to 6
move 3 from 9 to 5
move 2 from 6 to 2
move 1 from 5 to 2
move 3 from 5 to 4
move 3 from 4 to 1
move 7 from 9 to 6
move 4 from 6 to 1
move 1 from 1 to 8
move 3 from 6 to 9
move 1 from 8 to 7
move 1 from 9 to 6
move 4 from 1 to 2
move 1 from 7 to 2
move 2 from 9 to 8
move 10 from 2 to 9
move 2 from 2 to 9
move 11 from 3 to 7
move 1 from 8 to 9
move 2 from 3 to 7
move 1 from 1 to 7
move 10 from 2 to 4
move 3 from 4 to 1
move 4 from 1 to 8
move 1 from 6 to 5
move 6 from 7 to 9
move 3 from 9 to 1
move 1 from 5 to 1
move 4 from 4 to 2
move 5 from 2 to 1
move 1 from 2 to 7
move 2 from 7 to 6
move 1 from 2 to 1
move 2 from 9 to 1
move 3 from 4 to 7
move 1 from 3 to 7
move 2 from 8 to 3
move 2 from 6 to 5
move 2 from 5 to 8
move 10 from 7 to 2
move 6 from 9 to 1
move 1 from 7 to 3
move 2 from 8 to 9
move 7 from 3 to 7
move 7 from 3 to 9
move 1 from 8 to 9
move 6 from 2 to 8
move 13 from 9 to 1
move 6 from 9 to 8
move 2 from 2 to 7
move 3 from 7 to 1
move 1 from 8 to 1
move 1 from 1 to 6
move 16 from 1 to 4
move 2 from 7 to 5
move 12 from 4 to 9
move 4 from 8 to 6
move 2 from 5 to 1
move 8 from 8 to 4
move 2 from 4 to 5
move 1 from 8 to 6
move 4 from 6 to 8
move 19 from 1 to 9
move 3 from 8 to 5
move 1 from 6 to 9
move 2 from 2 to 1
move 10 from 4 to 9
move 1 from 1 to 2
move 2 from 1 to 5
move 4 from 7 to 9
move 1 from 8 to 2
move 1 from 2 to 6
move 7 from 5 to 4
move 11 from 9 to 8
move 1 from 4 to 3
move 10 from 8 to 1
move 1 from 2 to 3
move 29 from 9 to 3
move 2 from 6 to 5
move 1 from 5 to 3
move 5 from 9 to 3
move 1 from 8 to 9
move 1 from 9 to 3
move 6 from 4 to 6
move 1 from 5 to 1
move 1 from 6 to 3
move 2 from 1 to 5
move 1 from 9 to 5
move 37 from 3 to 2
move 3 from 6 to 2
move 1 from 6 to 2
move 1 from 6 to 4
move 3 from 1 to 3
move 2 from 1 to 6
move 35 from 2 to 1
move 1 from 6 to 8
move 5 from 1 to 8
move 7 from 1 to 6
move 5 from 3 to 7
move 1 from 8 to 7
move 3 from 7 to 5
move 4 from 2 to 9
move 1 from 2 to 1
move 1 from 4 to 3
move 3 from 7 to 1
move 1 from 3 to 6
move 1 from 1 to 9
move 5 from 9 to 2
move 18 from 1 to 3
move 6 from 1 to 8
move 6 from 3 to 7
move 4 from 8 to 6
move 4 from 6 to 7
move 9 from 7 to 8
move 3 from 2 to 7
move 4 from 6 to 1
move 3 from 5 to 3
move 3 from 2 to 5
move 3 from 6 to 1
move 4 from 7 to 4
move 6 from 5 to 9
move 3 from 1 to 9
move 1 from 6 to 1
move 15 from 8 to 2
move 1 from 8 to 5
move 3 from 4 to 8
move 1 from 5 to 1
move 1 from 6 to 5
move 11 from 3 to 9
move 12 from 2 to 3
move 3 from 8 to 1
move 15 from 1 to 2
move 8 from 9 to 4
move 8 from 4 to 9
move 4 from 2 to 5
move 1 from 4 to 6
move 1 from 2 to 8
move 1 from 6 to 7
move 4 from 3 to 1
move 1 from 8 to 5
move 5 from 3 to 9
move 14 from 9 to 2
move 1 from 7 to 4
move 4 from 1 to 3
move 1 from 4 to 7
move 8 from 3 to 7
move 8 from 7 to 5
move 1 from 7 to 9
move 3 from 3 to 2
move 7 from 9 to 8
move 1 from 9 to 5
move 2 from 8 to 5
move 7 from 5 to 4
move 4 from 9 to 2
move 6 from 4 to 3
move 18 from 2 to 5
move 1 from 4 to 7
move 15 from 5 to 4
move 1 from 4 to 6
move 2 from 2 to 7
move 3 from 8 to 5
move 1 from 7 to 3
move 8 from 2 to 6
move 4 from 2 to 3
move 1 from 7 to 5
move 3 from 4 to 6
move 5 from 6 to 9
move 8 from 5 to 6
move 2 from 4 to 3
move 7 from 4 to 2
move 2 from 8 to 5
move 7 from 5 to 6
move 3 from 5 to 8
move 1 from 8 to 9
move 13 from 3 to 8
move 2 from 2 to 7
move 9 from 8 to 9
move 6 from 8 to 5
move 5 from 5 to 2
move 2 from 7 to 8
move 9 from 2 to 5
move 1 from 7 to 5
move 1 from 5 to 7
move 21 from 6 to 2
move 1 from 7 to 8
move 3 from 8 to 9
move 1 from 4 to 2
move 23 from 2 to 7
move 8 from 9 to 8
move 20 from 7 to 4
move 3 from 7 to 2
move 1 from 2 to 7
move 1 from 6 to 7
move 3 from 5 to 4
move 8 from 5 to 9
move 2 from 7 to 1
move 1 from 8 to 7
move 4 from 2 to 4
move 2 from 8 to 7
move 2 from 8 to 2
move 1 from 7 to 6
move 3 from 9 to 7
move 2 from 2 to 7
move 5 from 7 to 1
move 8 from 9 to 6
move 15 from 4 to 3
move 4 from 4 to 7
move 6 from 1 to 4
move 11 from 3 to 4
move 8 from 6 to 1
move 24 from 4 to 7
move 6 from 1 to 8
move 27 from 7 to 3
move 2 from 7 to 8
move 5 from 8 to 3
move 4 from 8 to 4
move 1 from 8 to 6
move 1 from 6 to 9
move 1 from 6 to 5
move 2 from 4 to 2
move 1 from 8 to 1
move 1 from 5 to 2
move 4 from 1 to 6
move 1 from 7 to 5
move 1 from 5 to 8
move 1 from 8 to 7
move 1 from 7 to 8
move 1 from 8 to 1
move 1 from 2 to 3
move 2 from 4 to 8
move 7 from 9 to 6
move 2 from 8 to 1
move 3 from 3 to 8
move 3 from 1 to 8
move 2 from 2 to 3
move 1 from 4 to 1
move 1 from 1 to 8
move 5 from 8 to 3
move 8 from 6 to 2
move 1 from 9 to 4
move 2 from 4 to 8
move 2 from 8 to 3
move 2 from 6 to 2
move 33 from 3 to 2
move 2 from 8 to 7
move 1 from 6 to 1
move 1 from 1 to 7
move 2 from 3 to 8
move 2 from 8 to 4
move 1 from 4 to 8
move 2 from 7 to 2
move 2 from 3 to 7
move 12 from 2 to 1
move 1 from 8 to 4
move 1 from 4 to 8
move 1 from 4 to 3
move 1 from 8 to 2
move 3 from 7 to 2
move 37 from 2 to 7
move 1 from 1 to 7
move 12 from 7 to 1
move 13 from 1 to 7
move 1 from 3 to 4
move 35 from 7 to 6
move 1 from 4 to 5
move 3 from 7 to 4
move 1 from 5 to 7
move 2 from 3 to 4
move 23 from 6 to 9
move 3 from 1 to 5
move 3 from 3 to 7
move 1 from 3 to 6
move 2 from 5 to 3
move 23 from 9 to 8
move 2 from 4 to 9
move 16 from 8 to 2
move 2 from 7 to 3
move 1 from 5 to 8
move 3 from 7 to 6
move 1 from 9 to 8
move 3 from 8 to 1
move 1 from 9 to 1
move 11 from 6 to 5
move 2 from 4 to 1
move 4 from 8 to 6
move 16 from 2 to 3
move 9 from 1 to 9
move 1 from 8 to 4
move 3 from 9 to 3
move 1 from 1 to 4
move 1 from 9 to 4
move 7 from 5 to 2
move 6 from 2 to 5
move 1 from 8 to 6
move 22 from 3 to 7
move 8 from 5 to 8
move 4 from 4 to 9
move 2 from 1 to 8
move 16 from 7 to 2
move 1 from 3 to 5
move 14 from 2 to 7
move 2 from 2 to 4
move 6 from 9 to 3