Date

Summary

In this post, I will introduce some problems related to date. 

Details

Is Leap Year

bool is_leap(int y) {
    if (y % 400 == 0) {
        return true;
    } else if (y % 100 == 0) {
        return false;
    } else {
        return y % 4 == 0;
    }
}

Days of the Year

vector<int> days = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int day_of_year(string date) {
    // date: "1900-12-21"
    int year = stoi(date.substr(0, 4));
    int month = stoi(date.substr(5, 2));
    int day = stoi(date.substr(8, 2));
    int result = 0;
    for (int m = 1; m < month; ++m) {
        result += days[m];
        if (m == 2 && is_leap(year)) {
            result++;
        }
    }
    result += day;
    return result;
}

Days from 1900

int day_since_1900(string date) {
    // date: "1900-12-21"
    int year = stoi(date.substr(0, 4));
    int result = 0;
    for (int y = 1900; y < year; ++y) {
        result += is_leap(y) ? 366 : 365;
    }
    result += day_of_year(date);
    return result;
}

Days Between Dates

int daysBetweenDates(string date1, string date2) {
    return abs(day_since_1900(date1) - day_since_1900(date2));
}