Multiplicative Inverse mod 26

Problem

Return the multiplicative inverse of a modulo 26, meaning the x in 1..25 with (a * x) % 26 == 1. Return -1 when no inverse exists.

Hint

An inverse exists exactly when gcd(a, 26) = 1.

case 1

in: [1]

expected: 1

case 2

in: [3]

expected: 9

case 3

in: [5]

expected: 21

case 4

in: [2]

expected: -1

case 5

in: [15]

expected: 7

case 6

in: [11]

expected: 19

Starter codePython

def mod_inverse_26(a):
    # Your code here
    pass

6 test cases · run your code against them in the editor