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111
2021/d17/ex1/ex1.py
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#!/usr/bin/env python
import itertools
import math
import sys
from typing import Iterator, List, NamedTuple
class Point(NamedTuple):
x: int
y: int
class Probe(NamedTuple):
position: Point
velocity: Point
class Area(NamedTuple):
min: Point
max: Point
def solve(input: List[str]) -> int:
def parse(line: str) -> Area:
x_range = line.split("x=")[1].split(",")[0]
y_range = line.split("y=")[1]
min_x, max_x = map(int, x_range.split(".."))
min_y, max_y = map(int, y_range.split(".."))
# Sanity check
assert min_x <= max_x
assert min_y <= max_y
return Area(Point(min_x, min_y), Point(max_x, max_y))
def trajectory(p: Probe) -> Iterator[Probe]:
def step(p: Probe) -> Probe:
def drag(x: int) -> int:
if x < 0:
return x + 1
if x > 0:
return x - 1
return 0
def gravity(y: int) -> int:
return y - 1
pos, vel = p
new_pos = Point(pos.x + vel.x, pos.y + vel.y)
new_vel = Point(drag(vel.x), gravity(vel.y))
return Probe(new_pos, new_vel)
while True:
yield (p := step(p))
def hits_target(probe: Probe, area: Area) -> bool:
# Too lazy to find an actual good condition on this loop, early break is enough
for p in trajectory(probe):
x, y = p.position
# Early exit when we cannot possibly get to the area
if y < area.min.y and p.velocity.y <= 0:
break
if x < area.min.x and p.velocity.x <= 0:
break
if x > area.max.x and p.velocity.x >= 0:
break
# Keep going if we're not in bounds
if x < area.min.x or x > area.max.x:
continue
if y < area.min.y or y > area.max.y:
continue
# We are in the area
return True
return False
def find_velocities(area: Area) -> Iterator[Point]:
position = Point(0, 0)
assert area.min.y < 0 # Sanity check, due to lower bound in loop
# Can't overshoot after a single step
for vx in range(0, area.max.x + 1):
# Can't overshoot after a single step, symmetric velocity when coming down
for vy in range(area.min.y, abs(area.min.y) + 1):
velocity = Point(vx, vy)
if hits_target(Probe(position, velocity), area):
yield velocity
def highest_point(velocity: Point) -> Point:
# When the y velocity is negative, the height can only go down
of_interest = itertools.takewhile(
lambda p: p.velocity.y >= 0, trajectory(Probe(Point(0, 0), velocity))
)
points = [p.position for p in of_interest]
return max(points, key=lambda p: p.y, default=Point(0, 0))
target_area = parse(input[0])
velocities = set(find_velocities(target_area))
return max(highest_point(v).y for v in velocities)
def main() -> None:
input = [line.strip() for line in sys.stdin.readlines()]
print(solve(input))
if __name__ == "__main__":
main()

1
2021/d17/ex1/input
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target area: x=79..137, y=-176..-117

103
2021/d17/ex2/ex2.py
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#!/usr/bin/env python
import itertools
import math
import sys
from typing import Iterator, List, NamedTuple
class Point(NamedTuple):
x: int
y: int
class Probe(NamedTuple):
position: Point
velocity: Point
class Area(NamedTuple):
min: Point
max: Point
def solve(input: List[str]) -> int:
def parse(line: str) -> Area:
x_range = line.split("x=")[1].split(",")[0]
y_range = line.split("y=")[1]
min_x, max_x = map(int, x_range.split(".."))
min_y, max_y = map(int, y_range.split(".."))
# Sanity check
assert min_x <= max_x
assert min_y <= max_y
return Area(Point(min_x, min_y), Point(max_x, max_y))
def trajectory(p: Probe) -> Iterator[Probe]:
def step(p: Probe) -> Probe:
def drag(x: int) -> int:
if x < 0:
return x + 1
if x > 0:
return x - 1
return 0
def gravity(y: int) -> int:
return y - 1
pos, vel = p
new_pos = Point(pos.x + vel.x, pos.y + vel.y)
new_vel = Point(drag(vel.x), gravity(vel.y))
return Probe(new_pos, new_vel)
while True:
yield (p := step(p))
def hits_target(probe: Probe, area: Area) -> bool:
# Too lazy to find an actual good condition on this loop, early break is enough
for p in trajectory(probe):
x, y = p.position
# Early exit when we cannot possibly get to the area
if y < area.min.y and p.velocity.y <= 0:
break
if x < area.min.x and p.velocity.x <= 0:
break
if x > area.max.x and p.velocity.x >= 0:
break
# Keep going if we're not in bounds
if x < area.min.x or x > area.max.x:
continue
if y < area.min.y or y > area.max.y:
continue
# We are in the area
return True
return False
def find_velocities(area: Area) -> Iterator[Point]:
position = Point(0, 0)
assert area.min.y < 0 # Sanity check, due to lower bound in loop
# Can't overshoot after a single step
for vx in range(0, area.max.x + 1):
# Can't overshoot after a single step, symmetric velocity when coming down
for vy in range(area.min.y, abs(area.min.y) + 1):
velocity = Point(vx, vy)
if hits_target(Probe(position, velocity), area):
yield velocity
target_area = parse(input[0])
velocities = set(find_velocities(target_area))
return len(velocities)
def main() -> None:
input = [line.strip() for line in sys.stdin.readlines()]
print(solve(input))
if __name__ == "__main__":
main()

1
2021/d17/ex2/input
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target area: x=79..137, y=-176..-117