modular_exponential.py

"""
Modular Exponential.
Modular exponentiation is a type of exponentiation performed over a modulus.
For more explanation, please check
https://en.wikipedia.org/wiki/Modular_exponentiation
"""

"""Calculate Modular Exponential."""


defmodular_exponential(base: int, power: int, mod: int):
"""
 >>> modular_exponential(5, 0, 10)
 1
 >>> modular_exponential(2, 8, 7)
 4
 >>> modular_exponential(3, -2, 9)
 -1
 """

ifpower<0:
return-1
base%=mod
result=1

whilepower>0:
ifpower&1:
result= (result*base) %mod
power=power>>1
base= (base*base) %mod

returnresult


defmain():
"""Call Modular Exponential Function."""
print(modular_exponential(3, 200, 13))


if__name__=="__main__":
importdoctest

doctest.testmod()

main()