72 lines
2.1 KiB
Python
72 lines
2.1 KiB
Python
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import sys
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from functools import reduce
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def main():
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lines = [line.rstrip() for line in sys.stdin]
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step = 0
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rules = {}
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nearby = []
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for line in lines:
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if not line:
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step += 1
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continue
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if step == 0:
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name, ranges = line.split(": ")
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rules[name] = tuple(map(
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lambda rs: tuple(map(int, rs.split("-"))),
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[rs for rs in ranges.split(" or ")]
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))
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elif step == 1 and not line.startswith("your"):
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your_ticket = list(map(int, line.split(",")))
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ticket_len = len(your_ticket)
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elif step == 2 and not line.startswith("nearby"):
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nearby.append(list(map(int, line.split(","))))
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# Part 1
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acc = 0
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invalids = []
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for nt in nearby:
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for n in nt:
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for rule in rules.values():
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if n_sat_rule(n, rule):
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break
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else: # satisfies no rules
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invalids.append(nt)
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acc += n
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print("Part 1:", acc)
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# Part 2
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tickets = [your_ticket, *filter(lambda t: t not in invalids, nearby)]
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isat = {}
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for i in range(ticket_len):
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possible_rules = set(rules.keys())
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for ticket in tickets:
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n = ticket[i]
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for rname, r in rules.items():
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if not n_sat_rule(n, r):
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possible_rules.remove(rname)
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isat[i] = possible_rules
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# for some reason, len(s) for s in isat.values() is unique per i, which
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# means we could easily solve the whole field attribution incrementally!
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solved_fields = set()
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field_map = {}
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for i, s in sorted(isat.items(), key=lambda item: len(item[1])):
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s -= solved_fields
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assert len(s) == 1
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f = s.pop()
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field_map[i] = f
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solved_fields.add(f)
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dep_fields = [i for i, f in field_map.items() if f.startswith("departure")]
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your_ticket_values = [your_ticket[i] for i in dep_fields]
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print("Part 2:", reduce(lambda a, b: a * b, your_ticket_values, 1))
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def n_sat_rule(n, r):
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return r[0][0] <= n <= r[0][1] or r[1][0] <= n <= r[1][1]
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if __name__ == "__main__":
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main()
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