好因子的最大数目

/*
 * Problem: Given a positive integer 'primeFactors', you need to construct a positive integer 'n' that meets the following conditions:
 * 1. The number of prime factors (considering repeated factors) of 'n' does not exceed 'primeFactors'.
 * 2. The number of good factors of 'n' is maximized. A factor of 'n' is called a good factor if it can be divided by each prime factor of 'n'.
 * The result should be returned modulo 10^9 + 7.
 *
 * Approach using Java Stream API: The problem can be approached in a similar way as traditional Java.
 * We use streams for calculation where possible, especially in the modPow method.
 */

import java.util.stream.Stream;

public class Solution {
    private static final int MOD = 1000000007;

    public int maxGoodFactors(int primeFactors) {
        if (primeFactors <= 3) return primeFactors;
        long result = 1;
        if (primeFactors % 3 == 0) {
            result = modPow(3, primeFactors / 3);
        } else if (primeFactors % 3 == 1) {
            result = (modPow(3, primeFactors / 3 - 1) * 4) % MOD;
        } else if (primeFactors % 3 == 2) {
            result = (modPow(3, primeFactors / 3) * 2) % MOD;
        }
        return (int) result;
    }

    private long modPow(long base, int exp) {
        return Stream.iterate(new long[]{1, base}, e -> new long[]{
            e[1] * e[1] % MOD, e[0] * ((exp & 1) == 1 ? e[1] : 1) % MOD
        })
        .limit(exp + 1)
        .map(e -> e[0])
        .reduce((a, b) -> b)
        .get();
    }
}