From 81c4073f32053644800834932162580f194d92c8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Anders=20Engl=C3=B6f=20Ytterstr=C3=B6m?= <yttan@fastmail.se>
Date: Tue, 6 May 2025 23:53:56 +0200
Subject: [PATCH] Solve 2017:25 "The Halting Problem"

---
 2017-python/solutions/day_25.py | 46 +++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 2017-python/solutions/day_25.py

diff --git a/2017-python/solutions/day_25.py b/2017-python/solutions/day_25.py
new file mode 100644
index 0000000..201bda3
--- /dev/null
+++ b/2017-python/solutions/day_25.py
@@ -0,0 +1,46 @@
+from solutions import BaseSolution
+from collections import defaultdict
+import re
+
+
+class Solution(BaseSolution):
+    input_file = "25.txt"
+
+    def __str__(self):
+        return "Day 25: The Halting Problem"
+
+    def solve(self, puzzle_input):
+        T = defaultdict(int)
+        p = 0
+
+        hd, *states = puzzle_input.split("\n\n")
+        S = int(re.findall(r"(\d+) steps", hd)[0])
+        s = re.findall(r"state (\w)\.", hd)[0]
+        P = {}
+        for state in states:
+            k = re.findall(r"state (\w)\:", state)[0]
+            v = [int(n) for n in re.findall(r"value (\d)\.", state)]
+            d = re.findall(r"(left|right)\.", state)
+            t = re.findall(r"state (\w)\.", state)
+            P[k] = (v[0], d[0], t[0], v[1], d[1], t[1])
+
+        for _ in range(S):
+            v0, d0, s0, v1, d1, s1 = P[s]
+            match T[p]:
+                case 0:
+                    T[p] = v0
+                    s = s0
+                    p += 1 if d0 == "right" else -1
+                case 1:
+                    T[p] = v1
+                    s = s1
+                    p += 1 if d1 == "right" else -1
+        return sum(T.values())
+
+    def solve_again(self, puzzle_input):
+        return "*"
+
+
+if __name__ == "__main__":
+    solution = Solution()
+    solution.show_results()