2023.10

challenges/2023/10-pipeMaze/README.md

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+# [Day 10: Pipe Maze](https://adventofcode.com/2023/day/10)

challenges/2023/10-pipeMaze/main.py

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+import sys
+import time
+
+
+Coordinate = tuple[int, int]
+
+
+def parse(instr: str) -> tuple[dict[Coordinate, str], Coordinate]:
+    s_loc = None
+    res = {}
+
+    for y, line in enumerate(instr.splitlines()):
+        for x, char in enumerate(line):
+            coord = (x, y)
+            
+            if char == "S":
+                s_loc = coord
+            
+            res[coord] = char
+
+    assert s_loc is not None
+    return res, s_loc
+
+
+acceptable_moves = {
+    "-": {
+        (-1, 0): ["L", "F", "-"],
+        (1, 0): ["7", "J", "-"],
+    },
+    "|": {
+        (0, -1): ["7", "F", "|"],
+        (0, 1): ["J", "L", "|"],
+    },
+}
+
+acceptable_moves["L"] = {
+    (c := (0, -1)): acceptable_moves["|"][c],
+    (c := (1, 0)): acceptable_moves["-"][c],
+}
+
+acceptable_moves["J"] = {
+    (c := (0, -1)): acceptable_moves["|"][c],
+    (c := (-1, 0)): acceptable_moves["-"][c],
+}
+
+acceptable_moves["F"] = {
+    (c := (0, 1)): acceptable_moves["|"][c],
+    (c := (1, 0)): acceptable_moves["-"][c],
+}
+
+acceptable_moves["7"] = {
+    (c := (0, 1)): acceptable_moves["|"][c],
+    (c := (-1, 0)): acceptable_moves["-"][c],
+}
+
+acceptable_moves["S"] = {
+    **acceptable_moves["|"], **acceptable_moves["-"]
+}
+
+
+def apply_coord_delta(a: Coordinate, b: Coordinate) -> Coordinate:
+    aa, ab = a
+    ba, bb = b
+    return aa + ba, ab + bb
+
+
+def check_coord(grid: dict[Coordinate, str], coord: Coordinate, vals: list[str]) -> bool:
+    v = grid.get(coord)
+    if v is None:
+        return False
+
+    if v in vals:
+        return True
+
+    return False
+
+
+def get_loop_boundary(grid: dict[Coordinate, str], start: Coordinate) -> dict[Coordinate, int]:
+    visited = {start: 0}
+    frontier = [start]
+
+    while frontier:
+        coord = frontier.pop(0)
+        char = grid[coord]
+        
+        for c in acceptable_moves.get(char, {}):
+            c_must_be = acceptable_moves[char][c]
+            c = apply_coord_delta(coord, c)
+            if c not in grid or c in visited:
+                continue
+            if check_coord(grid, c, c_must_be):
+                frontier.append(c)
+                visited[c] = visited[coord] + 1
+
+    return visited
+
+
+def one(instr: str):
+    loop_boundary = get_loop_boundary(*parse(instr))
+    return max(loop_boundary.values())
+
+
+def area(p):
+    # https://stackoverflow.com/a/451482
+    # HMM. I BARELY UNDERSTAND THIS.
+    return 0.5 * abs(sum(x0*y1 - x1*y0 for ((x0, y0), (x1, y1)) in zip(p, p[1:] + [p[0]])))
+
+
+def two(instr: str):
+    grid, start_coord = parse(instr)
+    loop_boundary = get_loop_boundary(grid, start_coord)
+
+    # This hilarious thing turns the loop boundary (dict of points with their
+    # distances away from the origin) and orders them into a contiguous
+    # sequence of points that represents the geometry of the shape.
+
+    cands = {}
+
+    for key in loop_boundary:
+        cands[loop_boundary[key]] = cands.get(loop_boundary[key], []) + [key]
+
+    keys = cands.keys()
+    res = []
+
+    for key in sorted(keys):
+        res.append(cands[key][0])
+
+    for key in reversed(sorted(keys)):
+        if len(cands[key]) < 2:
+            continue
+        res.append(cands[key][1])
+
+    # The area includes the size of the line itself, which we don't want. And
+    # an extra one that I don't understand the source of.
+
+    return int(area(res) - max(loop_boundary.values()) + 1)
+
+
+def _debug(*args, **kwargs):
+    kwargs["file"] = sys.stderr
+    print(*args, **kwargs)
+
+
+if __name__ == "__main__":
+    if len(sys.argv) < 2 or sys.argv[1] not in ["1", "2"]:
+        print("Missing day argument", file=sys.stderr)
+        sys.exit(1)
+    inp = sys.stdin.read().strip()
+    if sys.argv[1] == "1":
+        print(one(inp))
+    else:
+        print(two(inp))

challenges/2023/10-pipeMaze/tests.json

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+{
+    "1": [
+        {
+            "is": "4",
+            "input": ".....\n.S-7.\n.|.|.\n.L-J.\n.....\n\n"
+        },
+        {
+            "is": "8",
+            "input": "..F7.\n.FJ|.\nSJ.L7\n|F--J\nLJ...\n"
+        }
+    ],
+    "2": [
+        {
+            "is": "4",
+            "input": "..........\n.S------7.\n.|F----7|.\n.||....||.\n.||....||.\n.|L-7F-J|.\n.|..||..|.\n.L--JL--J.\n..........\n"
+        },
+        {
+            "is": "4",
+            "input": "...........\n.S-------7.\n.|F-----7|.\n.||.....||.\n.||.....||.\n.|L-7.F-J|.\n.|..|.|..|.\n.L--J.L--J.\n...........\n\n"
+        },
+        {
+            "is": "10",
+            "input": "FF7FSF7F7F7F7F7F---7\nL|LJ||||||||||||F--J\nFL-7LJLJ||||||LJL-77\nF--JF--7||LJLJ7F7FJ-\nL---JF-JLJ.||-FJLJJ7\n|F|F-JF---7F7-L7L|7|\n|FFJF7L7F-JF7|JL---7\n7-L-JL7||F7|L7F-7F7|\nL.L7LFJ|||||FJL7||LJ\nL7JLJL-JLJLJL--JLJ.L\n\n"
+        },
+        {
+            "is": "8",
+            "input": ".F----7F7F7F7F-7....\n.|F--7||||||||FJ....\n.||.FJ||||||||L7....\nFJL7L7LJLJ||LJ.L-7..\nL--J.L7...LJS7F-7L7.\n....F-J..F7FJ|L7L7L7\n....L7.F7||L7|.L7L7|\n.....|FJLJ|FJ|F7|.LJ\n....FJL-7.||.||||...\n....L---J.LJ.LJLJ...\n\n"
+        }
+    ]
+}