HJ06 J6 质数因子

​​J6 质数因子​​

#include <iostream>
#include <list>

class HJ06 {
private:
    double static sqrt(int num, double err = 1e-15) {
        if (num < 0) {return -1;}
        auto c = (double)num;
        double t = c;
        while (std::abs(t-c/t) > err * t) {
            t = (c/t + t) / 2.0;
        }
        return t;
    }
public:
    static std::list<int> primeFactors(int num) {
        std::list<int> ans;
        int max;

        while (num % 2 == 0) {
            num /= 2;
            ans.push_back(2);
        }
        while (num % 3 == 0) {
            num /= 3;
            ans.push_back(3);
        }
        max = int(sqrt(num, 1e-2) + 0.5);
        // for (int i = 5; i*i <= num; i++) {
        for (int i = 5; i <= max; i++) {
            while (num % i == 0) {
                num /= i;
                ans.push_back(i);
            }
        }
        if (num != 1) {
            ans.push_back(num);
        }
        return ans;
    }
};

int main() {
    // int n = 180;
    // int n = 2000000014;
    int n = 0;
    std::cin >> n;

    std::list<int> factors = HJ06::primeFactors(n);
    auto it = factors.begin(); // std::list<int>::const_iterator
    std::cout << *it++;
    for (; it != factors.end(); ++it) {
        std::cout << " " << *it;
    }
    return 0;
}

float 四舍五入取近似值可以 +0.5 再转int

​​HJ7 取近似值​​