day06 part2

advent/advent2024/day06.py

@@ -11,31 +11,52 @@
 def main():
     lines = advent.get_input_lines()
     grid = np.array([[c for c in line] for line in lines])
-    start = np.where(grid == "^")
+    start_position = np.where(grid == "^")
+    start = (start_position[0][0], start_position[1][0])
 
-    seen = run(grid, (start[0][0], start[1][0]))
-    advent.submit(1, len(seen))
+    looped, seen = run(grid, start)
+    unique = set([(x, y) for x, y, _ in seen])
+    advent.submit(1, len(unique))
+
+    count = 0
+    unique.remove(start)
+    for position in unique:
+        grid[position] = "#"
+        looped, _ = run(grid, start)
+        count += 1 if looped else 0
+        grid[position] = "."
+
+    advent.submit(2, count)
 
 
 def print_grid(grid: npt.NDArray[np.str_]):
     for row in range(grid.shape[0]):
         print("".join(grid[row]))
 
 
-def run(grid: npt.NDArray[np.str_], start: tuple[int, int]) -> set[tuple[int, int]]:
+def run(
+    grid: npt.NDArray[np.str_], start: tuple[int, int]
+) -> tuple[bool, set[tuple[int, int, int]]]:
     x, y = start
     dir = 0
-    seen: set[tuple[int, int]] = set()
-    seen.add((x, y))
+    seen: set[tuple[int, int, int]] = set()
     dx, dy = deltas[dir]
-    while 0 <= x + dx < grid.shape[0] and 0 <= y + dy < grid.shape[1]:
+    while (
+        0 <= x + dx < grid.shape[0]
+        and 0 <= y + dy < grid.shape[1]
+        and (x, y, dir) not in seen
+    ):
+        seen.add((x, y, dir))
         dx, dy = deltas[dir]
         if grid[(x + dx, y + dy)] == "#":
             dir = (dir + 1) % 4
         else:
             x, y = x + dx, y + dy
-            seen.add((x, y))
-    return seen
+    if (x, y, dir) in seen:
+        return True, seen
+
+    seen.add((x, y, dir))
+    return False, seen
 
 
 if __name__ == "__main__":