day 16

1 files changed, 85 insertions, 0 deletions

diff --git a/16.py b/16.py
new file mode 100644
index 0000000..aaf6d0c
--- /dev/null
+++ b/16.py
@@ -0,0 +1,85 @@
+from collections import deque
+from enum import Enum, auto
+from sys import stdin
+
+
+class Dir(Enum):
+    NORTH = auto()
+    EAST = auto()
+    SOUTH = auto()
+    WEST = auto()
+
+
+def step(direction: Dir, pos: tuple[int, int]) -> tuple[int, int]:
+    match direction:
+        case Dir.NORTH:
+            return pos[0], pos[1] - 1
+        case Dir.EAST:
+            return pos[0] + 1, pos[1]
+        case Dir.SOUTH:
+            return pos[0], pos[1] + 1
+        case Dir.WEST:
+            return pos[0] - 1, pos[1]
+
+
+inp = [line.rstrip("\n") for line in stdin]
+
+
+def solve(inp: list[str], start: tuple[Dir, tuple[int, int]]) -> int:
+    beams: deque[tuple[Dir, tuple[int, int]]] = deque((start,))
+    old_beams: set[tuple[Dir, tuple[int, int]]] = set()
+    covered: set[tuple[int, int]] = set()
+
+    def add(direction: Dir, pos: tuple[int, int]):
+        t = (direction, step(direction, pos))
+        if t in old_beams:
+            return
+        old_beams.add(t)
+        beams.append(t)
+
+    while beams:
+        direction, pos = beams.popleft()
+        x, y = pos
+        if x < 0 or x >= len(inp[0]) or y < 0 or y >= len(inp):
+            continue
+        covered.add(pos)
+        c = inp[y][x]
+        if (
+            c == "."
+            or (c == "-" and direction in {Dir.EAST, Dir.WEST})
+            or (c == "|" and direction in {Dir.NORTH, Dir.SOUTH})
+        ):
+            add(direction, pos)
+        elif c == "|":
+            add(Dir.NORTH, pos)
+            add(Dir.SOUTH, pos)
+        elif c == "-":
+            add(Dir.EAST, pos)
+            add(Dir.WEST, pos)
+        else:
+            mapping: dict[tuple[str, Dir], Dir] = {
+                ("/", Dir.NORTH): Dir.EAST,
+                ("/", Dir.EAST): Dir.NORTH,
+                ("/", Dir.SOUTH): Dir.WEST,
+                ("/", Dir.WEST): Dir.SOUTH,
+                ("\\", Dir.NORTH): Dir.WEST,
+                ("\\", Dir.EAST): Dir.SOUTH,
+                ("\\", Dir.SOUTH): Dir.EAST,
+                ("\\", Dir.WEST): Dir.NORTH,
+            }
+            add(mapping[c, direction], pos)
+
+    return len(covered)
+
+
+print(solve(inp, (Dir.EAST, (0, 0))))
+
+p2 = 0
+for x in range(len(inp[0])):
+    p2 = max(p2, solve(inp, (Dir.SOUTH, (x, 0))))
+    p2 = max(p2, solve(inp, (Dir.NORTH, (x, len(inp)))))
+
+for y in range(len(inp)):
+    p2 = max(p2, solve(inp, (Dir.EAST, (0, y))))
+    p2 = max(p2, solve(inp, (Dir.WEST, (len(inp[0]), y))))
+print(p2)