2016: d14: ex2: add solution

2016/d14/ex2/ex2.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python
+
+import functools
+import hashlib
+import itertools
+import sys
+
+
+def solve(input: str) -> int:
+    def hash(n: int, salt: str) -> str:
+        key = salt + str(n)
+        for _ in range(2016 + 1):
+            key = hashlib.md5(key.encode()).hexdigest()
+        return key
+
+    def find_triplet_char(input: str) -> str | None:
+        for i in range(0, len(input) - 2):
+            a, b, c = input[i], input[i + 1], input[i + 2]
+            if a == b and b == c:
+                return a
+        return None
+
+    salt = input.strip()
+    hashed_salt = functools.cache(functools.partial(hash, salt=salt))
+    cur_key = 0
+    for i in itertools.count():
+        candidate = hashed_salt(i)
+        if (triplet_char := find_triplet_char(candidate)) is None:
+            continue
+        for j in range(i + 1, i + 1000 + 1):
+            if (triplet_char * 5) in hashed_salt(j):
+                cur_key += 1
+                if cur_key == 64:
+                    return i
+                break
+    assert False  # Sanity check
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()