Day 10: much more efficient solution

2019/day10.py

@@ -1,46 +1,31 @@
 import math
 
+import numpy as np
+
 
 def main():
     with open("day10.txt", "rt") as input_file:
         amap = [line.rstrip() for line in input_file.readlines()]
 
-    ast_positions = []
-    for x, line in enumerate(amap):
-        for y, value in enumerate(line):
+    asteroids = []
+    for y, line in enumerate(amap):
+        for x, value in enumerate(line):
             if value == "#":
-                ast_positions.append((x, y))
+                asteroids.append((x, y))
 
     best_vis = 0
-    for pos in ast_positions:
-        best_vis = max(best_vis, num_visible_asts(ast_positions, pos))
-
-    print("Best visibility is", best_vis)
+    best_pos = None
+    for pos in asteroids:
+        vis = num_visible_asts(asteroids, pos)
+        if vis > best_vis:
+            best_vis, best_pos = vis, pos
+    print(f"Best visibility is {best_vis} at {best_pos}.")
 
 def num_visible_asts(asts, ref):
-    count = 0
-    for ast in asts:
-        if ast[0] == ref[0] and ast[1] == ref[1]:
-            continue
-        if is_visible(asts, ref, ast):
-            count += 1
-    return count
-
-def is_visible(asts, ref, target):
-    for ast in asts:
-        if ast[0] == ref[0] and ast[1] == ref[1]:
-            continue
-        if ast[0] == target[0] and ast[1] == target[1]:
-            continue
-        if is_on_line(ref, target, ast):
-            return False
-    return True
-
-def is_on_line(a, b, p):
-    return math.isclose(dist(a, b), dist(a, p) + dist(b, p))
-
-def dist(a, b):
-    return math.sqrt((a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2)
+    asts = asts.copy()
+    asts.remove(ref)
+    angles = [np.angle(np.complex(ast[0] - ref[0], ast[1] - ref[1])) for ast in asts]
+    return len(set(angles))
 
 
 if __name__ == "__main__":