day 23

2020/23/23.py

@@ -0,0 +1,45 @@
+def read_file():
+	with open("input.txt","r") as f:
+		return list(map(int,list(f.read())))
+
+def play(cups, rounds):
+	current = cups[0]
+	next_cup = {c:n for c, n in zip(cups, cups[1:] + [cups[0]])}
+	for _ in range(rounds):
+		# pickup next 3 cups
+		c1 = next_cup[current]
+		c2 = next_cup[c1]
+		c3 = next_cup[c2]
+		# select a destination cup (-1 until found, wraps around)
+		destination = current - 1 if current > 1 else len(cups)
+		while destination in [c1, c2, c3]:
+			destination = destination - 1 if destination > 1 else len(cups)
+		# add cups back
+		next_cup[current] = next_cup[c3]
+		next_cup[c3] = next_cup[destination]
+		next_cup[destination] = c1
+		# select a new current cup (next)
+		current = next_cup[current]
+	# rebuild cups from next_cup
+	cup = 1
+	new_cups = []
+	for _ in range(len(cups)):
+		cup = next_cup[cup]
+		new_cups.append(cup)
+	return new_cups
+
+def part1(cups):
+	cups = play(cups, 100)
+	return "".join(str(c) for c in cups[:-1])
+
+def part2(cups):
+	cups += list(range(10,1_000_001))
+	cups = play(cups,10_000_000)
+	return cups[0] * cups[1]
+
+def main():
+	cups = read_file()
+	print(part1(cups), part2(cups))
+
+if __name__ == "__main__":
+	main()

2020/23/input.txt

@@ -0,0 +1 @@
+653427918