2023 d22: Add original solution

Author: mebeim

2023/original_solutions/day22.py

@@ -0,0 +1,172 @@
+#!/usr/bin/env python3
+
+from utils.all import *
+
+advent.setup(2023, 22)
+DEBUG = 'debug' in map(str.lower, sys.argv)
+fin = advent.get_input() if not DEBUG else io.StringIO('''\
+1,0,1~1,2,1
+0,0,2~2,0,2
+0,2,3~2,2,3
+0,0,4~0,2,4
+2,0,5~2,2,5
+0,1,6~2,1,6
+1,1,8~1,1,9
+''')
+
+def draw_xz(space):
+	g = {}
+	maxz = max(map(itemgetter(2), space))
+	for x in range(10): g[maxz - 0 + 1, x] = '-'
+	for (x, _, z), ident in space.items(): g[maxz - z + 1, x] = ident
+	dump_sparse_matrix(g)
+
+def draw_yz(space):
+	g = {}
+	maxz = max(map(itemgetter(1), space))
+	for y in range(10): g[maxz - 0 + 1, y] = '-'
+	for (_, y, z), ident in space.items(): g[maxz - z + 1, y] = ident
+	dump_sparse_matrix(g)
+
+def fall_one(space, ident, ax, ay, az, bx, by, bz):
+	assert (az != bz) + (ax != bx) + (ay != by) <= 1
+	# eprint('brick', ident, (ax, ay, az, bx, by, bz), 'falls')
+
+	below = set()
+
+	if ax != bx:
+		# Find first z (from az down) for which x,ay,z is occupied
+		for minz in range(az, -1, -1):
+			for x in autorange(ax, bx):
+				# eprint('>', (x, ay, minz))
+				if (x, ay, minz) in space:
+					# eprint('> obstacle', (x, ay, minz))
+					below.add(space[x, ay, minz])
+
+			if below:
+				break
+
+		minz += 1
+		# eprint(minz)
+		for x in autorange(ax, bx):
+			space[x, ay, minz] = ident
+	elif ay != by:
+		# Find first z (from az down) for which ax,y,z is occupied
+		for minz in range(az, -1, -1):
+			for y in autorange(ay, by):
+				# eprint('>', (ax, y, minz))
+				if (ax, y, minz) in space:
+					# eprint('> obstacle', (ax, y, minz))
+					below.add(space[ax, y, minz])
+
+			if below:
+				break
+
+		minz += 1
+		# eprint(minz)
+		for y in autorange(ay, by):
+			space[ax, y, minz] = ident
+	else:
+		zlo = min(az, bz)
+
+		# Find first z (from z down) for which ax,ay,z is occupied
+		for minz in range(zlo, -1, -1):
+			# eprint('>', (ax, ay, minz))
+			if (ax, ay, minz) in space:
+				# eprint('> obstacle', (ax, ay, minz))
+				below = {space[ax, ay, minz]}
+				break
+
+		minz += 1
+		# eprint(minz)
+
+		delta = zlo - minz
+		az -= delta
+		bz -= delta
+
+		for z in autorange(az, bz):
+			space[ax, ay, z] = ident
+
+	return below
+
+
+def fall():
+	bricks.sort(key=lambda b: min(b[2], b[5]))
+	space = {}
+	supports = {}
+
+	for identifier, b in enumerate(bricks):
+		below = fall_one(space, identifier, *b)
+		supports[identifier] = below
+		# draw_xz(space)
+		# draw_yz(space)
+
+	# for x in sorted(supports):
+	# 	print(x, bricks[x], 'supported by', supports[x])
+
+	deletable = set(range(len(bricks)))
+
+	# I cannot delete a brick if it's the only one supporting some other brick
+	for below in supports.values():
+		if len(below) == 1:
+			deletable.discard(next(iter(below)))
+
+	return deletable, supports
+
+
+lines = read_lines(fin)
+bricks = []
+
+for line in lines:
+	coords = extract_ints(line)
+	bricks.append(coords)
+
+deletable, supports = fall()
+
+ans1 = len(deletable)
+advent.print_answer(1, ans1)
+
+
+def find_falling(supported_by, supports, root):
+	falling = {root}
+	q = deque([root])
+
+	while q:
+		brick = q.popleft()
+
+		for a in supported_by[brick]:
+			if all(s in falling for s in supports[a]):
+				falling.add(a)
+				q.append(a)
+
+	falling.discard(root)
+	return falling
+
+not_deletable = set(range(len(bricks))) - deletable
+assert len(deletable) + len(not_deletable) == len(bricks)
+
+#   33333
+#   2   4
+# 111   4
+# 0     4
+# not_deletable = {0, 1}
+# supports = {
+# 	0: set(),
+# 	1: {0},
+# 	2: {1},
+# 	3: {2,4},
+# 	4: set(),
+# }
+
+supported_by = defaultdict(set)
+for brick, below in supports.items():
+	for b in below:
+		supported_by[b].add(brick)
+
+tot = 0
+for brick in not_deletable:
+	falling = find_falling(supported_by, supports, brick)
+	# print('deleting', brick, 'would make these fall:', falling)
+	tot += len(falling)
+
+advent.print_answer(2, tot)