From 0e937ae7fe7cbd4b9b491421705d556f38a00114 Mon Sep 17 00:00:00 2001
From: Marvin Borner
Date: Thu, 21 Dec 2023 11:59:41 +0100
Subject: pls run this on supercomputer, thx

---
 2023/21/solve.py | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

(limited to '2023')

diff --git a/2023/21/solve.py b/2023/21/solve.py
index df17878..9aca201 100644
--- a/2023/21/solve.py
+++ b/2023/21/solve.py
@@ -4,6 +4,9 @@ L = {
     for (j, c) in enumerate(l.strip())
 }
 
+W = max(j for (i, j) in L.keys())
+H = max(i for (i, j) in L.keys())
+
 
 def solve1():
     LIM = 64
@@ -28,4 +31,29 @@ def solve1():
     print(res)
 
 
+def solve2():
+    LIM = 26501365
+
+    res = 0
+    s = [(i, j) for (i, j) in L if L[(i, j)] == "S"][0]
+    q = [(s, 0)]
+    v = set()
+    while q:
+        p, n = q.pop(0)
+        if n == LIM + 1:
+            continue
+
+        for move in [(0, 1), (1, 0), (0, -1), (-1, 0)]:
+            np = (p[0] + move[0], p[1] + move[1])
+            _np = (np[0] % (H + 1), np[1] % (W + 1))
+            if _np not in L or np in v or L[_np] == "#":
+                continue
+            q.append((np, n + 1))
+            v.add(np)
+            if n % 2:
+                res += 1
+    print(res)
+
+
 solve1()
+solve2()
-- 
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