102 lines
2.8 KiB
Python
Executable file
102 lines
2.8 KiB
Python
Executable file
#!/usr/bin/env python
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import sys
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from typing import Iterator, List, NamedTuple
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class Point(NamedTuple):
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x: int
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y: int
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class Probe(NamedTuple):
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position: Point
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velocity: Point
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class Area(NamedTuple):
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min: Point
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max: Point
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def solve(input: List[str]) -> int:
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def parse(line: str) -> Area:
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x_range = line.split("x=")[1].split(",")[0]
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y_range = line.split("y=")[1]
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min_x, max_x = map(int, x_range.split(".."))
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min_y, max_y = map(int, y_range.split(".."))
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# Sanity check
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assert min_x <= max_x
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assert min_y <= max_y
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return Area(Point(min_x, min_y), Point(max_x, max_y))
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def trajectory(p: Probe) -> Iterator[Probe]:
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def step(p: Probe) -> Probe:
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def drag(x: int) -> int:
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if x < 0:
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return x + 1
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if x > 0:
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return x - 1
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return 0
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def gravity(y: int) -> int:
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return y - 1
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pos, vel = p
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new_pos = Point(pos.x + vel.x, pos.y + vel.y)
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new_vel = Point(drag(vel.x), gravity(vel.y))
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return Probe(new_pos, new_vel)
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while True:
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yield (p := step(p))
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def hits_target(probe: Probe, area: Area) -> bool:
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# Too lazy to find an actual good condition on this loop, early break is enough
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for p in trajectory(probe):
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x, y = p.position
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# Early exit when we cannot possibly get to the area
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if y < area.min.y and p.velocity.y <= 0:
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break
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if x < area.min.x and p.velocity.x <= 0:
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break
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if x > area.max.x and p.velocity.x >= 0:
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break
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# Keep going if we're not in bounds
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if x < area.min.x or x > area.max.x:
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continue
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if y < area.min.y or y > area.max.y:
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continue
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# We are in the area
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return True
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return False
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def find_velocities(area: Area) -> Iterator[Point]:
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position = Point(0, 0)
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assert area.min.y < 0 # Sanity check, due to lower bound in loop
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# Can't overshoot after a single step
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for vx in range(0, area.max.x + 1):
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# Can't overshoot after a single step, symmetric velocity when coming down
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for vy in range(area.min.y, abs(area.min.y) + 1):
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velocity = Point(vx, vy)
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if hits_target(Probe(position, velocity), area):
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yield velocity
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target_area = parse(input[0])
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velocities = set(find_velocities(target_area))
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return len(velocities)
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def main() -> None:
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input = [line.strip() for line in sys.stdin.readlines()]
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print(solve(input))
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if __name__ == "__main__":
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main()
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