Solve 2019 day 10

2019/d10.py

@@ -0,0 +1,102 @@
+from lib import get_data, Grid2D
+from math import gcd, atan2, pi
+
+
+def angle(a1, a2):
+    dy = a1[0] - a2[0]
+    dx = a2[1] - a1[1]
+    a = (atan2(dx, dy) + 2 * pi) % (2 * pi)
+    return a
+
+
+def dist(a1, a2):
+    return abs(a1[0] - a2[0]) + abs(a1[1] - a2[1])
+
+
+def part_1(data):
+    g = Grid2D(data)
+    asts = g.find("#")
+    asts_set = set(asts)
+
+    best_ast = None
+    visible_max = 0
+    for a in asts:
+        visible = 0
+        for other in asts:
+            if a == other:
+                continue
+            x1, x2 = a[0], other[0]
+            y1, y2 = a[1], other[1]
+
+            if y1 == y2:
+                for x in range(min(x1, x2) + 1, max(x1, x2)):
+                    if (x, y1) in asts_set:
+                        break
+                else:
+                    visible += 1
+            elif x1 == x2:
+                for y in range(min(y1, y2) + 1, max(y1, y2)):
+                    if (x1, y) in asts_set:
+                        break
+                else:
+                    visible += 1
+            else:
+                dx = abs(x1 - x2)
+                dy = abs(y1 - y2)
+                g = gcd(dx, dy)
+                dx //= g
+                dy //= g
+
+                x, y = x1, y1
+                if x2 < x1:
+                    dx = -dx
+                if y2 < y1:
+                    dy = -dy
+
+                blocked = False
+                while True:
+                    x += dx
+                    y += dy
+                    if (x, y) == (x2, y2):
+                        break
+                    if (x, y) in asts_set:
+                        blocked = True
+                        break
+                if not blocked:
+                    visible += 1
+
+        if visible > visible_max:
+            visible_max = visible
+            best_ast = a
+
+    assert best_ast is not None
+    print(visible_max)
+
+    other_asts = [a for a in asts if a != best_ast]
+    removed_count = 0
+    while True:
+        removed = set()
+        other_asts = sorted(
+            other_asts, key=lambda a: (angle(best_ast, a), dist(best_ast, a))
+        )
+        lowest_angle = -1
+        for a in other_asts:
+            current_angle = angle(best_ast, a)
+            if current_angle > lowest_angle:
+                removed.add(a)
+                lowest_angle = current_angle
+                removed_count += 1
+
+            if removed_count == 200:
+                print(a[1] * 100 + a[0])
+                return
+        other_asts = [a for a in other_asts if a not in removed]
+
+
+def main():
+    data = get_data(__file__)
+    part_1(data)
+
+
+if __name__ == "__main__":
+    main()