1904. 你完成的完整对局数

class Solution {
public:
    int numberOfRounds(string loginTime, string logoutTime) {
        int h1 = stoi(loginTime.substr(0, 2));
        int m1 = stoi(loginTime.substr(3, 2));
        int h2 = stoi(logoutTime.substr(0, 2));
        int m2 = stoi(logoutTime.substr(3, 2));

        int a1 = h1 * 60 + m1;
        int a2 = h2 * 60 + m2;

        if(a1 > a2) a2 += 24 * 60;

        int a = ceil(double(a1) / 15);//上取整
        int b = floor(double(a2) / 15);//下取整

        return max(0, b - a);
    }
};