Ruby

def part1 = find_unique_string(4)
def part2 = find_unique_string(14)

private

def find_unique_string(length)
  batches = file.chars.each_cons(length).to_a
  seq = batches.find { |chars| chars.uniq.length == length }
  batches.index(seq) + length
end

def file = File.read("input/06.txt")