LeetCode 372. Super Pow

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原题网址：https://leetcode.com/problems/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 = 2b = [3]Result: 8

Example2:

a = 2b = [1,0]Result: 1024

方法：分析模的特点，若a % 1337 = n * 1337 + m，b % 1337 = p * 1337 + q，则a*b % 1337 = m * q % 1337

public class Solution {    private int[] mod;    private int mod(int a, int p) {        if (mod[p] > 0) return mod[p];        if (p == 0) {            mod[p] = a % 1337;            return mod[p];        }        int m = 1;        for(int i = 0; i < 10; i++) {            m *= mod(a, p - 1);            m %= 1337;        }        mod[p] = m;        return mod[p];    }    public int superPow(int a, int[] b) {        if (a % 191 == 0 && a % 7 == 0) return 0;        mod = new int[b.length];        int m = 1;        for(int i = 0; i < b.length; i++) {            for(int j = 1; j <= b[i]; j++) {                m *= mod(a, b.length - 1 - i);                m %= 1337;            }        }        return m;    }}

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