Solve problem 381

2026-06-18 15:42:03 -04:00
parent 5c9e9d775f
commit 908cdb9a7e
2 changed files with 57 additions and 0 deletions
@@ -230,3 +230,18 @@ def cache(f):
        return r
    return func_cached

+
+def ext_gcd(a: int, b: int) -> tuple[int, int, int]:
+    if a == 0:
+        return (b, 0, 1)
+    else:
+        gcd, x, y = ext_gcd(b % a, a)
+        return (gcd, y - (b // a) * x, x)
+
+
+def modinv(a: int, b: int) -> int:
+    gcd, x, _ = ext_gcd(a, b)
+    if gcd != 1:
+        raise Exception('Modular inverse does not exist')
+    else:
+        return x % b