Add day 8 solutions

1 files changed, 55 insertions, 0 deletions

diff --git a/2021/08/puzzle-2.py b/2021/08/puzzle-2.py
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+++ b/2021/08/puzzle-2.py
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+#!/usr/bin/env python3
+
+import itertools
+
+
+def solve(nums: list[str]) -> int:
+	nummap: dict[str, set[str]] = {}
+
+	# First pass, find the easy patterns. From these 4 patterns you can determine all other ones
+	for n in nums:
+		nummap[[0, 0, 1, 7, 4, 0, 0, 8][len(n)]] = set(n)
+
+	# Second pass, here we use the magic of sets to work out all the other numbers from the 4
+	# that we found above
+	for n in nums:
+		match len((s := set(n))):
+			# 2, 3, or 5
+			case 5:
+				# 1 is a subset of 3 and none of the others
+				if nummap[1].issubset(s):
+					nummap[3] = s
+				# 4 is a subset of 5 union with 1 but not 2 union with 1
+				elif set(nummap[4]).issubset(set(s).union(set(nummap[1]))):
+					nummap[5] = s
+				else:
+					nummap[2] = s
+			# 0, 6, or 9
+			case 6:
+				# 1 is a subset of 6 but not 0 or 9
+				if not set(nummap[1]).issubset(set(s)):
+					nummap[6] = s
+				# 4 is a subset of 9 but not 0
+				elif set(nummap[4]).issubset(set(s)):
+					nummap[9] = s
+				else:
+					nummap[0] = s
+	
+	nums = nums[nums.index("|") + 1 :]
+
+	acc = 0
+	for n, (k, v) in itertools.product(nums, nummap.items()):
+		if set(v) == set(n):
+			acc = acc * 10 + int(k)
+	return acc
+
+
+def main() -> None:
+	with open("input", "r", encoding="utf-8") as f:
+		data = list(map(lambda l: l.strip().split(), f.readlines()))
+
+	print(sum(solve(line) for line in data))
+
+
+if __name__ == "__main__":
+	main()