aoc/2021/03/03.py

report = []

with open("input.txt") as f:
	lines = f.read().split('\n')
for line in lines:
	report.append(line)

gamma = ''
for i in range(len(report[0])):
	ones_count = 0
	for number in report:
		if number[i] == '1':
			ones_count += 1

	half = len(report) / 2
	if ones_count > half:
		gamma += '1'
	else:
		gamma += '0'

power = 2 ** len(gamma) - 1
gamma = int(gamma, 2)
epsilon = power - gamma
part1 = gamma * epsilon
print(part1)


o2_candidates = set()
co2_candidates = set()
for number in report:
	o2_candidates.add(number)
	co2_candidates.add(number)

for i in range(len(report[0])):
	if len(o2_candidates) == 1:
		break
	# first pass: count the bits in each position
	ones_count = 0
	zeros_count = 0
	for number in o2_candidates:
		if number[i] == '0':
			zeros_count += 1
		else:
			ones_count += 1
	# Keep 1, unless 0 is more common.
	if zeros_count > ones_count:
		keep = '0'
	else:
		keep = '1'
	# second pass: filter out the candidates
	for number in o2_candidates.copy():
		if number[i] != keep:
			o2_candidates.remove(number)

for i in range(len(report[0])):
	if len(co2_candidates) == 1:
		break
	# first pass: count the bits in each position
	ones_count = 0
	zeros_count = 0
	for number in co2_candidates:
		if number[i] == '0':
			zeros_count += 1
		else:
			ones_count += 1
	# Keep 0, unless 1 is less common.
	if ones_count < zeros_count:
		keep = '1'
	else:
		keep = '0'
	# second pass: filter out the candidates
	for number in co2_candidates.copy():
		if number[i] != keep:
			co2_candidates.remove(number)

o2 = int(o2_candidates.pop(), 2)
co2 = int(co2_candidates.pop(), 2)
part2 = o2 * co2
print(part2)