Fixed horizontal and diagonal ray casting

src/AoC_2023/Dazbo's_Advent_of_Code_2023.ipynb

@@ -3570,6 +3570,35 @@
     "        \"S\": [\"N\", \"E\", \"S\", \"W\"] # start location\n",
     "    }\n",
     "    \n",
+    "    def infer_start_type(self, loop: list[Point]) -> str:\n",
+    "        \"\"\" Determine the pipe type of the start point. It does this by determining\n",
+    "        the two connected pipes in the loop. From their directions and types, we know what the S\n",
+    "        must be.\n",
+    "        \"\"\"\n",
+    "        start_posn = len(loop) // 2\n",
+    "        assert self.value_at_point(loop[start_posn]) == \"S\", \"Middle of the loop should be start\"\n",
+    "        \n",
+    "        dirs = set()\n",
+    "        for vector in [loop[start_posn+1] - loop[start_posn], loop[start_posn-1] - loop[start_posn]]:\n",
+    "            (x, y) = vector.x, vector.y\n",
+    "            match (x, y):\n",
+    "                case Vectors.N.value:\n",
+    "                    dirs.add(\"N\")\n",
+    "                case Vectors.E.value:\n",
+    "                    dirs.add(\"E\")\n",
+    "                case Vectors.S.value:\n",
+    "                    dirs.add(\"S\")\n",
+    "                case Vectors.W.value:\n",
+    "                    dirs.add(\"W\")\n",
+    "                case _:\n",
+    "                    assert False, \"Invalid direction\"\n",
+    "        \n",
+    "        for pipe_type, directions in PipeGrid.directions_for_pipe.items():\n",
+    "            if dirs == set(directions):\n",
+    "                return pipe_type\n",
+    "        \n",
+    "        assert False, \"No valid pipe type found\"                    \n",
+    "        \n",
     "    def valid_neighbours_for_loop_pipe(self, point: Point) -> list[Point]:\n",
     "        \"\"\" Get valid neighbours, given a current location that is the main pipe loop. \"\"\"\n",
     "        valid = []\n",
@@ -3893,6 +3922,8 @@
     "    This function constructs the loop path starting from the 'furthest' point, which is\n",
     "    the most distant point from the start in the grid, back to the starting point. The path\n",
     "    is constructed in two halves and then combined.\n",
+    "    \n",
+    "    Note, the start point is therefore the point in the middle.\n",
     "    \"\"\"\n",
     "    start = next(point for point in grid.all_points()\n",
     "            if grid.value_at_point(point) == \"S\")\n",
@@ -4033,7 +4064,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Altternative Solutions and Useful Resources\n",
+    "### Alternative Solutions and Useful Resources\n",
     "\n",
     "There are a few other ways to solve this problem. \n",
     "\n",
@@ -4100,9 +4131,11 @@
     "    loop_path = get_loop_path(grid, furthest, came_from) # get complete enclosed main loop\n",
     "    loop_points = set(loop_path)\n",
     "    cleaned_grid = remove_junk_parts(grid, loop_points)    \n",
-    "    logger.debug(f\"\\n{cleaned_grid}\")\n",
+    "    # logger.debug(f\"\\n{cleaned_grid}\")\n",
     "\n",
-    "    # //todo replace S with appropriate char. Determine S based on the prev and next directions\n",
+    "    # update \"S\" to be actual pipe type\n",
+    "    start_type = grid.infer_start_type(loop_path)\n",
+    "    cleaned_grid.set_value_at_point(loop_path[len(loop_path)//2], start_type)\n",
     "    \n",
     "    inside = 0\n",
     "    # sweep each low, from left to right\n",
@@ -4126,7 +4159,9 @@
     "    loop_points = set(loop_path)\n",
     "    cleaned_grid = remove_junk_parts(grid, loop_points)\n",
     "    \n",
-    "    # //todo replace S with appropriate char. Determine S based on the prev and next directions\n",
+    "    # update \"S\" to be actual pipe type\n",
+    "    start_type = grid.infer_start_type(loop_path)\n",
+    "    cleaned_grid.set_value_at_point(loop_path[len(loop_path)//2], start_type)\n",
     "        \n",
     "    inside = 0\n",
     "    # sweep diagonally, in the right/down direction\n",
@@ -4220,14 +4255,6 @@
     "\n",
     "sample_answers = [4, 4, 8, 10]\n",
     "\n",
-    "# Shoelace + Pick's Theorem\n",
-    "for func in (d10_with_shoelace_and_picks, \n",
-    "             d10_with_horizontal_ray_casting,\n",
-    "             d10_with_diagonal_ray_casting,\n",
-    "             d10_with_scale_up):\n",
-    "    logger.info(f\"Solving with {func.__name__}() ...\")\n",
-    "    test_and_run_with_solve(func)\n",
-    "\n",
     "def test_and_run_with_solve(solve:func):\n",
     "    for curr_input, curr_ans in zip(sample_inputs, sample_answers):\n",
     "        curr_grid = parse_grid(curr_input.splitlines())\n",
@@ -4240,7 +4267,16 @@
     "\n",
     "    grid = parse_grid(input_data)\n",
     "    soln = func(grid, furthest, came_from)\n",
-    "    logger.info(f\"Part 2 soln={soln}\")"
+    "    logger.info(f\"Part 2 soln={soln}\")\n",
+    "    \n",
+    "# Shoelace + Pick's Theorem\n",
+    "for func in (d10_with_shoelace_and_picks, \n",
+    "             d10_with_horizontal_ray_casting,\n",
+    "             d10_with_diagonal_ray_casting,\n",
+    "             d10_with_scale_up):\n",
+    "    logger.info(f\"Solving with {func.__name__}() ...\")\n",
+    "    test_and_run_with_solve(func)\n",
+    "\n"
    ]
   },
   {