Add 2024 day 20 solutions

3 files changed, 44 insertions, 0 deletions

diff --git a/2024/20/.gitignore b/2024/20/.gitignore
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+++ b/2024/20/.gitignore
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+puzzle-[12].py
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diff --git a/2024/20/Makefile b/2024/20/Makefile
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+++ b/2024/20/Makefile
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+include ../../Makefiles/py.mk
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diff --git a/2024/20/puzzles.py b/2024/20/puzzles.py
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index 0000000..8727f6e
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+++ b/2024/20/puzzles.py
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+#!/usr/bin/python3
+
+def main() -> None:
+	points: set[complex] = set()
+
+	with open("input", "r") as f:
+		for i, line in enumerate(f.readlines()):
+			for j, char in enumerate(line):
+				if char in "#\n":
+					continue
+				points.add(pos := complex(j, i))
+				if char == 'S':
+					start = pos
+
+	print(solve(start, points, 100, 2 if PUZZLE_PART == 1 else 20))
+
+def solve(
+	pos: complex,
+	points: set[complex],
+	minsave: int,
+	maxcheat: int,
+) -> int:
+	path: list[complex] = []
+	while points:
+		path.append(pos)
+		for v⃗ in [1, -1, 1j, -1j]:
+			if (p := pos + v⃗) in points:
+				break
+		points.remove(pos)
+		pos = p
+
+	cnt = 0
+	for i, p1 in enumerate(path):
+		off = i + minsave
+		for j, p2 in enumerate(path[off + 2:], off + 2):
+			d = p1 - p2
+			if abs(d.real) + abs(d.imag) <= min(j - off, maxcheat):
+				cnt += 1
+	return cnt
+
+if __name__ == "__main__":
+	main()
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