Leetcode 372. Super Pow

Your task is to calculate a^b mod 1337 where a is a positive integer and b is an extremely large positive integer given in the form of an array.

Example1:

a = 2
b = [3]

Result: 8

Example2:

a = 2
b = [1,0]

Result: 1024

使用公式 c = ab  =>  c mod d = [a mod d * b mod d] mod d

所以a^423 mod d = (a^100)^4 * (a ^10)^2 * a^3

 class Solution(object):
     def superPow(self, a, b):
         """
         :type a: int
         :type b: List[int]
         :rtype: int
         """
         ans = 1
         mod = 1337
         for i in b[::-1]:
             ans = ans * a ** i % mod
             a = a ** 10 % mod
         return ans % mod