99 lines
2.5 KiB
Python
99 lines
2.5 KiB
Python
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#!/usr/bin/env python
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import dataclasses
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import functools
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import sys
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from collections.abc import Iterable
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from typing import NamedTuple, Optional
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class Point(NamedTuple):
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x: int
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y: int
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@classmethod
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def from_input(cls, input: str) -> "Point":
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assert input.startswith("x=") # Sanity check
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x, y = input.split(", ")
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return cls(int(x.split("=")[-1]), int(y.split("=")[-1]))
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class Interval(NamedTuple):
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start: int
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end: int
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def as_set(self) -> set[int]:
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return set(range(self.start, self.end + 1))
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def merge_intervals(intervals: Iterable[Interval]) -> list[Interval]:
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intervals = sorted(intervals)
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res = [intervals[0]]
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for candidate in intervals[1:]:
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# Range is inclusive in both end, so add 1 to end in case of near miss
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if (res[-1].end + 1) >= candidate.start:
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new_end = max(res[-1].end, candidate.end)
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res[-1] = Interval(res[-1].start, new_end)
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else:
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res.append(candidate)
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return res
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def distance(a: Point, b: Point) -> int:
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return abs(a.x - b.x) + abs(a.y - b.y)
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@dataclasses.dataclass
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class SensorData:
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pos: Point
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beacon: Point
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@classmethod
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def from_input(cls, input: str) -> "SensorData":
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assert input.startswith("Sensor at x=") # Sanity check
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mid = input.index(":")
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sensor, beacon = input[:mid], input[mid:]
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return cls(
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Point.from_input(sensor[sensor.index("x") :]),
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Point.from_input(beacon[beacon.index("x") :]),
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)
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@functools.cached_property
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def safe_range(self) -> int:
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return distance(self.pos, self.beacon)
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def scan_row(self, row: int) -> Optional[Interval]:
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distance = abs(row - self.pos.y)
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dx = self.safe_range - distance
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if dx < 0:
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return None
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return Interval(self.pos.x - dx, self.pos.x + dx)
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def solve(input: list[str]) -> int:
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def points_without_sos(data: list[SensorData], row: int) -> list[Interval]:
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intervals = (d.scan_row(row) for d in data)
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return merge_intervals(i for i in intervals if i is not None)
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data = [SensorData.from_input(line) for line in input]
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beacons = {d.beacon for d in data}
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ROW = 2_000_000
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intervals = points_without_sos(data, ROW)
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return len(
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set.union(*(i.as_set() for i in intervals))
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- {b.x for b in beacons if b.y == ROW}
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)
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def main() -> None:
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input = sys.stdin.read().splitlines()
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print(solve(input))
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if __name__ == "__main__":
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main()
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