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Solve day 13 part 1 and nearly 2
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69
2020/day13_bus.py
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69
2020/day13_bus.py
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import enum
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import functools
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import math
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from typing import List, Dict
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def main(filename: str, expected_part_1: int = None, expected_part_2: int = None):
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print(f"\n+ Running on {filename}")
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with open(filename) as f:
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notes = f.read().strip().split("\n")
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counter_part_1 = solve_part_1(notes)
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print(f"1. Found {counter_part_1}")
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if expected_part_1:
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assert expected_part_1 == counter_part_1
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counter_part_2 = solve_part_2(notes)
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print(f"2. Found {counter_part_2}")
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if expected_part_2:
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assert expected_part_2 == counter_part_2
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def solve_part_1(notes) -> int:
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earliest = int(notes[0])
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buses = map(int, filter(lambda bus: bus != "x", notes[1].split(",")))
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min_delta = math.inf
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min_bus = None
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for bus in buses:
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delta = math.ceil(earliest / bus) * bus - earliest
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if delta < min_delta:
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min_delta = delta
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min_bus = bus
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return min_bus * min_delta
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def solve_part_2(notes) -> int:
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"""Works but far too slow for the real deal."""
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split = notes[1].split(",")
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buses = list(map(int, filter(lambda bus: bus != "x", split)))
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minutes = {} # type: Dict[int, int]
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biggest_bus = max(buses)
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biggest_bus_index = split.index(str(biggest_bus))
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for bus in buses:
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minutes[split.index(str(bus)) - biggest_bus_index] = bus
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found = False
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timestamp = 99999999999628
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while not found:
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timestamp += biggest_bus
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found = True
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for delta, bus in minutes.items():
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if (timestamp + delta) % bus != 0:
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found = False
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break
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return timestamp + min(minutes.keys())
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if __name__ == "__main__":
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main("inputs/day13-test1", 295, 1068781)
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main("inputs/day13-test2", None, 3417)
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main("inputs/day13-test3", None, 754018)
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main("inputs/day13-test4", None, 779210)
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main("inputs/day13-test5", None, 1261476)
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main("inputs/day13-test6", None, 1202161486)
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main("inputs/day13", 4315)
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2
2020/inputs/day13
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2
2020/inputs/day13
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1001938
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41,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,37,x,x,x,x,x,431,x,x,x,x,x,x,x,23,x,x,x,x,13,x,x,x,17,x,19,x,x,x,x,x,x,x,x,x,x,x,863,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,29
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2
2020/inputs/day13-test1
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2
2020/inputs/day13-test1
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939
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7,13,x,x,59,x,31,19
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2
2020/inputs/day13-test2
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2
2020/inputs/day13-test2
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939
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17,x,13,19
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2
2020/inputs/day13-test3
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2
2020/inputs/day13-test3
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939
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67,7,59,61
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2
2020/inputs/day13-test4
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2
2020/inputs/day13-test4
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939
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67,x,7,59,61
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2
2020/inputs/day13-test5
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2
2020/inputs/day13-test5
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939
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67,7,x,59,61
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2
2020/inputs/day13-test6
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2
2020/inputs/day13-test6
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939
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1789,37,47,1889
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