A-M baby

Task/Modular-inverse/Python/modular-inverse.py

@@ -0,0 +1,18 @@
+>>> def extended_gcd(aa, bb):
+    lastremainder, remainder = abs(aa), abs(bb)
+    x, lastx, y, lasty = 0, 1, 1, 0
+    while remainder:
+        lastremainder, (quotient, remainder) = remainder, divmod(lastremainder, remainder)
+        x, lastx = lastx - quotient*x, x
+        y, lasty = lasty - quotient*y, y
+    return lastremainder, lastx * (-1 if aa < 0 else 1), lasty * (-1 if bb < 0 else 1)
+
+>>> def modinv(a, m):
+	g, x, y = extended_gcd(a, m)
+	if g != 1:
+		raise ValueError
+	return x % m
+
+>>> modinv(42, 2017)
+1969
+>>>