cleanup and catchup

2021/03/03.py

@@ -2,12 +2,10 @@ report = []
 
 with open("input.txt") as f:
 	lines = f.read().split('\n')
-	for line in lines:
+for line in lines:
 	report.append(line)
 
 gamma = ''
-power = 2 ** len(report[0]) - 1
-
 for i in range(len(report[0])):
 	ones_count = 0
 	for number in report:
@@ -20,9 +18,62 @@ for i in range(len(report[0])):
 	else:
 		gamma += '0'
 
+power = 2 ** len(gamma) - 1
 gamma = int(gamma, 2)
 epsilon = power - gamma
 part1 = gamma * epsilon
 print(part1)
 
-o2 = co2 = 0
+
+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)