参考：

// greateast common divisor  ==> gcd// 辗转相除法 求 最大公约数// int big = a > b ? a : b;// int little = a < b ? a : b;int gcd(int big, int little){    if (big % little == 0){        return little;    }    return gcd(little, big%little);}void test(){    std::cout << "gcd(4,10)= " << gcd(4, 10) << std::endl;    std::cout << "gcd(123456, 7890)= " << gcd(123456, 7890) << std::endl;}/*gcd(4,10)= 2gcd(123456, 7890)= 6*/