Family Day update

Task/Modular-inverse/Prolog/modular-inverse.pro

@@ -0,0 +1,10 @@
+egcd(_, 0, 1, 0) :- !.
+egcd(A, B, X, Y) :-
+    divmod(A, B, Q, R),
+    egcd(B, R, S, X),
+    Y is S - Q*X.
+
+modinv(A, B, N) :-
+    egcd(A, B, X, Y),
+    A*X + B*Y =:= 1,
+    N is X mod B.

Task/Modular-inverse/Swift/modular-inverse.swift

@@ -0,0 +1,20 @@
+extension BinaryInteger {
+  @inlinable
+  public func modInv(_ mod: Self) -> Self {
+    var (m, n) = (mod, self)
+    var (x, y) = (Self(0), Self(1))
+
+    while n != 0 {
+      (x, y) = (y, x - (m / n) * y)
+      (m, n) = (n, m % n)
+    }
+
+    while x < 0 {
+      x += mod
+    }
+
+    return x
+  }
+}
+
+print(42.modInv(2017))