day17

Author: narimiran

README.md

@@ -41,7 +41,7 @@ Day 00: Helper file                                                        | [ao
 [Day 14: Extended Polymerization](http://adventofcode.com/2021/day/14)    | [day14.py](python/day14.py) | `Counter` to the rescue.
 [Day 15: Chiton](http://adventofcode.com/2021/day/15)                     | [day15.py](python/day15.py) | Dijkstra.
 [Day 16: Packet Decoder](http://adventofcode.com/2021/day/16)             | [day16.py](python/day16.py) | `iter` for some elegant stream implementation.
-[Day 17](http://adventofcode.com/2021/day/17)                             | [day17.py](python/day17.py) |
+[Day 17: Trick Shot](http://adventofcode.com/2021/day/17)                 | [day17.py](python/day17.py) | Analytical + brute force.
 [Day 18](http://adventofcode.com/2021/day/18)                             | [day18.py](python/day18.py) |
 [Day 19](http://adventofcode.com/2021/day/19)                             | [day19.py](python/day19.py) |
 [Day 20](http://adventofcode.com/2021/day/20)                             | [day20.py](python/day20.py) |

inputs/17.txt

@@ -0,0 +1 @@
+target area: x=124..174, y=-123..-86

python/day17.py

@@ -0,0 +1,26 @@
+from aoc import read_input_line, integers
+
+
+def move(x, y, vx, vy):
+    x += vx
+    y += vy
+    if vx > 0: vx -= 1
+    vy -= 1
+    return x, y, vx, vy
+
+
+def will_hit(vx, vy):
+    x, y = 0, 0
+    while x <= x2 and y >= y1:
+        x, y, vx, vy = move(x, y, vx, vy)
+        if x1 <= x <= x2 and y1 <= y <= y2:
+            return True
+    return False
+
+
+x1, x2, y1, y2 = integers(read_input_line(17))
+
+print(y1 * (y1+1) // 2)
+print(sum(will_hit(vx, vy)
+          for vx in range(x2+1)
+          for vy in range(y1, -y1)))