Advent of Code 2021 - Day 8

aoc_2021_08.py

# Always sort letters (= positions) alphabetically for comparison
def sort_(s):
  return "".join(sorted(s))

part_1 = 0
for seg in input_:
  signals = seg.split(' | ')[1].split(' ')
  for signal in signals:
    if len(signal) in [2, 3, 4, 7]:
      part_1 += 1

part_2 = 0
for seg in input_:
  signals_output = seg.split(' | ')

  signals = signals_output[0].split(' ')
  output = [sort_(signal) for signal in signals_output[1].split(' ')]

  translator = {
    1: [sort_(s) for s in signals if len(s) == 2][0],
    4: [sort_(s) for s in signals if len(s) == 4][0],
    7: [sort_(s) for s in signals if len(s) == 3][0],
    8: [sort_(s) for s in signals if len(s) == 7][0]
  }

  # Positions c and f are common to digits 1 and 7
  c_f = list(set(translator[7]) & set(translator[1]))

  # Positions b and d are the only present in digit 4 but not in digit 7
  b_d = list(set(translator[4]) - set(translator[7]))

  # Digit 3 is the only one with 5 segments and contains positions c and f
  translator[3] = [sort_(s) for s in signals if len(s) == 5 and c_f[0] in s and c_f[1] in s][0]

  # Digit 5 is the only one with 5 segments and contains positions b and d
  translator[5] = [sort_(s) for s in signals if len(s) == 5 and b_d[0] in s and b_d[1] in s][0]

  # Digit 2 is the remaining digit with 5 segments
  translator[2] = [sort_(s) for s in signals if len(s) == 5 and sort_(s) not in [translator[3], translator[5]]][0]

  # Digit 0 is the only one with 6 segments that does not contain _both_ positions b and d
  translator[0] = [sort_(s) for s in signals if len(s) == 6 and (b_d[0] not in s or b_d[1] not in s)][0]

  # Digit 6 is the only one with 6 segments that does not contain _both_ positions c and f
  translator[6] = [sort_(s) for s in signals if len(s) == 6 and (c_f[0] not in s or c_f[1] not in s)][0]

  # Digit 9 is the remaining digit with 6 segments
  translator[9] = [sort_(s) for s in signals if len(s) == 6 and sort_(s) not in [translator[0], translator[6]]][0]

  # Revert the dictionnary to easily access values
  inv_translator = {v: str(k) for k, v in translator.items()}
  
  # Convert the last 4 signals into an integer and sum it
  part_2 += int("".join([inv_translator[s] for s in output]))

print(part_1)
print(part_2)