51 lines
2.0 KiB
Python
51 lines
2.0 KiB
Python
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# https://tinyurl.com/5n934wef
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import collections, math
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# A 2d grid stored as a dict keyed on complex values
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grid = {
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x + y * 1j: e
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for y, l in enumerate(open("input.in").read().split("\n"))
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for x, e in enumerate(l)
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}
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# part_sum is the answer to problem 1
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# stars is a dictionary where the key will be star coordinates and the
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# values are a list of all adjacent numbers.
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part_sum, stars = 0, collections.defaultdict(list)
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for y in range(max(int(c.imag) for c in grid) + 1):
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# sym_adj is whether the current number is adjacent to a symbol
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# adj_stars is a set of all adjacent stars to the current number
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# cur_num is whatever the number we're currently building, zero otherwise
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sym_adj, adj_stars, cur_num = False, set(), 0
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for x in range(max(int(c.real) for c in grid) + 2):
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char = grid.get(x + y * 1j, ".")
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# When we see a number, we need to add it to the number we're constructing.
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# At the same time, we need to check if there are any adjacent symbols
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# and, if one of those symbols is a star, keep note of those coords
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if char.isnumeric():
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cur_num = cur_num * 10 + int(char)
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for x1 in range(-1, 2):
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for y1 in range(-1, 2):
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# Adding the x1, y1 offsets to our current x,y
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coord = x + y * 1j + x1 + y1 * 1j
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char = grid.get(coord, ".")
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sym_adj |= not char in "1234567890."
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if char == "*":
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adj_stars.add(coord)
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# When we see anything other than a number, we need to add the cur_num
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# to part_sum if we previously found an adjacent symbol. Additionally,
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# if there's an adjacent star, we add it to the stars dict.
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else:
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if cur_num and sym_adj:
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part_sum += cur_num
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for s in adj_stars:
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stars[s].append(cur_num)
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sym_adj, adj_stars, cur_num = False, set(), 0
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print(part_sum)
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print(sum(map(math.prod, [s for s in stars.values() if len(s) == 2])))
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