1 files changed, 64 insertions, 0 deletions
diff --git a/2023/23/part1.py b/2023/23/part1.py
new file mode 100644
index 0000000..555a5eb
--- /dev/null
+++ b/2023/23/part1.py
@@ -0,0 +1,64 @@
+# adapted from day 16
+
+L = {
+    (y, x): c
+    for y, l in enumerate(open("input").readlines())
+    for x, c in enumerate(l.strip())
+    if c != "#"
+}
+
+
+def oob(y, x, d):
+    return (y, x) not in L
+
+
+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)]
+
+    if ch == "^":
+        return [next(y, x, 0)]
+    if ch == ">":
+        return [next(y, x, 1)]
+    if ch == "v":
+        return [next(y, x, 2)]
+    if ch == "<":
+        return [next(y, x, 3)]
+
+    return [next(y, x, k) for k in range(4) if abs(d - k) != 2]
+
+
+def dfs(y, x, d):
+    end = list(L.keys())[-1]
+    longest = 0
+    ps = []
+    st = []
+    st.append((y, x, d, set(), 1))
+    while st:
+        y, x, d, v, p = st.pop()
+        v.add((y, x))
+        ns = neighbours(y, x, d)
+        for n in ns:
+            if n[:2] not in v and not oob(*n):
+                np = p + 1
+                st.append((*n, set(v), np))
+
+                if n[:2] == end:  # reached end
+                    ps.append(np)
+
+    return ps
+
+
+ps = dfs(0, 1, 2)
+mx = max(p for p in ps)
+print(mx - 1)