require_relative 'util'

# --- Day 10: Elves Look, Elves Say ---

# Today, the Elves are playing a game called look-and-say. They take
# turns making sequences by reading aloud the previous sequence and
# using that reading as the next sequence. For example, 211 is read as
# "one two, two ones", which becomes 1221 (1 2, 2 1s).

# Look-and-say sequences are generated iteratively, using the previous
# value as input for the next step. For each step, take the previous
# value, and replace each run of digits (like 111) with the number of
# digits (3) followed by the digit itself (1).

# For example:

# 1 becomes 11 (1 copy of digit 1).
# 11 becomes 21 (2 copies of digit 1).
# 21 becomes 1211 (one 2 followed by one 1).
# 1211 becomes 111221 (one 1, one 2, and two 1s).
# 111221 becomes 312211 (three 1s, two 2s, and one 1).

# Starting with the digits in your puzzle input, apply this process 40
# times. What is the length of the result?

input = '1113222113'

def look_and_say(input)
  input.each_char
       .slice_when { |x, y| x != y }
       .flat_map { |a| "#{a.length}#{a[0]}" }
       .join
end

def easy(input)
  40.times { input = look_and_say(input) }
  input.length
end

assert(look_and_say('1') == '11')
assert(look_and_say('11') == '21')
assert(look_and_say('21') == '1211')
assert(look_and_say('1211') == '111221')
assert(look_and_say('111221') == '312211')
puts "easy(input): #{easy(input)}"

# --- Part Two ---

# Neat, right? You might also enjoy hearing John Conway talking about
# this sequence (that's Conway of Conway's Game of Life fame).

# Now, starting again with the digits in your puzzle input, apply this
# process 50 times. What is the length of the new result?

def hard(input)
  50.times { input = look_and_say(input) }
  input.length
end

puts "hard(input): #{hard(input)}"