2022 Day 17 Python

2022/day17.py

@@ -0,0 +1,124 @@
+from helpers import *
+
+gas_cycles = read_day(17)
+sample_gas_cycles = '>>><<><>><<<>><>>><<<>>><<<><<<>><>><<>>'
+
+rocks = '''
+####
+
+.#.
+###
+.#.
+
+..#
+..#
+###
+
+#
+#
+#
+#
+
+##
+##
+'''.strip().split('\n\n')
+# rock_shapes = [np.array([[1 if c=='#' else 0 for c in line] for line in r.split('\n')], dtype=np.int8).T for r in rocks]
+rock_shapes = [np.fliplr(np.array([[1 if c=='#' else 0 for c in line] for line in r.split('\n')], dtype=np.int8).T) for r in rocks]
+
+def simulate_rockfall(gas_cycle: str, num_rocks=50000, debug=False) -> ArrayLike:  # returns height increment per rock
+	def p(message):
+		if debug:
+			print(message)
+
+	width = 7
+	height_5_rocks = 1+3+3+4+2
+	max_possible_height = (num_rocks//5 + 2) * height_5_rocks
+	len_gas_cycle = len(gas_cycle)
+
+	field = np.zeros((7, max_possible_height), dtype=np.int8)
+	height_increments = np.zeros(num_rocks, dtype=np.int8)
+	highest = 0
+	t = -1
+	for r in range(num_rocks):
+		rock_shape = rock_shapes[r%5]
+		r_width, r_height = rock_shape.shape
+
+		def check_collision(r_x, r_y):
+			r_x2 = r_x + r_width
+			r_y2 = r_y + r_height
+			if r_x < 0:
+				p(f'would hit left wall - {r_x, r_x2} at y={r_y}')
+				return True
+			if r_x2 > width:
+				p(f'would hit right wall - {r_x, r_x2} at y={r_y}')
+				return True
+			if r_y < 0:
+				p(f'would hit floor - {r_x, r_x2} at y={r_y}')
+				return True
+			return np.any(field[r_x:r_x2, r_y:r_y2] & rock_shape == 1)
+
+		# Spawn rock with bottom-left corner at x=2, y=highest+3  (y-up)
+		r_x = 2
+		r_y = highest + 3 
+		while True:
+			t += 1
+			if gas_cycle[t%len_gas_cycle] == '>':
+				if not check_collision(r_x+1, r_y):  # move right
+					r_x += 1
+					p('moved right')
+			else:
+				if not check_collision(r_x-1, r_y):  # move left
+					r_x -= 1
+					p('moved left')
+			# move down
+			if check_collision(r_x, r_y-1):
+				field[r_x:r_x+r_width, r_y:r_y+r_height] |= rock_shape
+				old_highest = highest
+				highest = max(highest, r_y+r_height)
+				height_increments[r] = highest - old_highest
+				break
+			else:
+				r_y -= 1
+				p('moved down')
+		p(f'rock #{r} landed, highest point {highest}, gas cycle {t}, rock shape ({r_width}x{r_height}) at {r_x},{r_y}')
+	return height_increments
+
+sample_incs = simulate_rockfall(sample_gas_cycles, 10000)
+incs = simulate_rockfall(gas_cycles, 30000)
+print(f'Part 1 (sample): {sample_incs[:2022].sum()}')
+print(f'Part 1: {incs[:2022].sum()}')
+
+
+def find_cycle_and_infer(increments: ArrayLike, search_cycle_length: int, target_index: int):
+	search_term = increments[search_cycle_length:search_cycle_length*2]
+	hits = []
+	for st in range(search_cycle_length*2, len(increments)-search_cycle_length):
+		if np.all(increments[st:st+search_cycle_length] == search_term):
+			hits.append(st)
+			print(f'Found loop starting at {st}')
+			if len(hits) > 2:
+				break
+	else:
+		print('no loop found!')
+		return
+
+	loop_len = hits[1]-hits[0]
+	loop_len2 = hits[2]-hits[1]
+	if loop_len2 == loop_len:
+		print(f'Confirmed loop of length {loop_len}')
+	else:
+		print(f'Mismatched loop lengths of {loop_len} and {loop_len2}!')
+		return
+
+	base_value = increments[:hits[0]].sum()
+	loop_values = increments[hits[0]:hits[1]].cumsum()
+	loop_total = loop_values[-1]
+
+	loops, remainder = divmod(target_index - hits[0], loop_len)
+	value = base_value + loop_total*loops
+	if remainder > 0:
+		value += loop_values[remainder-1]
+	return value
+
+print(f'Part 2 (sample): {find_cycle_and_infer(sample_incs, 1000, 1000000000000)}')
+print(f'Part 2: {find_cycle_and_infer(incs, 5000, 1000000000000)}')