OOB

1 files changed, 83 insertions, 0 deletions

diff --git a/2023/16/solve.py b/2023/16/solve.py
new file mode 100644
index 0000000..4be5d69
--- /dev/null
+++ b/2023/16/solve.py
@@ -0,0 +1,83 @@
+L = {
+    (y, x): c
+    for y, l in enumerate(open("input").readlines())
+    for x, c in enumerate(l.strip())
+}
+
+W = max(x for (_, x) in L.keys())
+H = max(y for (y, _) in L.keys())
+
+
+def oob(y, x, d):
+    return x > W or x < 0 or y > H or y < 0
+
+
+def next(y, x, d):
+    if d == 0:
+        return (y - 1, x, d)
+    if d == 1:
+        return (y, x + 1, d)
+    if d == 2:
+        return (y + 1, x, d)
+    if d == 3:
+        return (y, x - 1, d)
+
+
+def neighbours(y, x, d):
+    ch = L[(y, x)]
+
+    # rule 1
+    if ch == ".":
+        return [next(y, x, d)]
+
+    # rule 2
+    if ch == "/":
+        r = [1, 0, 3, 2]
+        return [next(y, x, r[d])]
+    if ch == "\\":
+        r = [3, 2, 1, 0]
+        return [next(y, x, r[d])]
+
+    # rule 3
+    if ch == "|" and d in [1, 3]:
+        return [(y - 1, x, 0), (y + 1, x, 2)]
+    if ch == "-" and d in [0, 2]:
+        return [(y, x + 1, 1), (y, x - 1, 3)]
+
+    # rule 4
+    if ch == "|" and d in [0, 2] or ch == "-" and d in [1, 3]:
+        return [next(y, x, d)]
+
+
+def visited(sy, sx, sd):
+    q = [(sy, sx, sd)]
+    v = set()
+    v.add(q[0])
+
+    while q:
+        y, x, d = q.pop(0)
+
+        ns = neighbours(y, x, d)
+        for n in ns:
+            if n not in v and not oob(*n):
+                v.add(n)
+                q.append(n)
+
+    return len(set((y, x) for (y, x, _) in v))
+
+
+def solve1():
+    print(visited(0, 0, 1))
+
+
+def solve2():
+    res = 0
+    for x in range(W):
+        res = max(res, visited(0, x, 2), visited(H, x, 0))
+    for y in range(H):
+        res = max(res, visited(y, 0, 1), visited(y, W, 3))
+    print(res)
+
+
+solve1()
+solve2()