题解 | #Day of Week#

#include <iostream>
#include <cstdio>

using namespace std;

/*
 * 二维数组保存平年和闰年0~12月份对应的天数
 */
int dayTable[2][13] = {
    {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},    //平年
    {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}     //闰年
};

/*
 * 星期名称的字符串
 */
char weekDayTable[8][15] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};


/*
 * 月份名称的字符串
 */
char monthTable[13][15] = {"", "January", "February", "March", "April", "May", "June", "July", "August", "September",
                           "October", "November", "December"
                          };

/**
 * 判断是否为闰年
 * @param year
 * @return
 */
int isLeapYear(int year) {
    //return (year & 3 == 0 && year % 100 != 0) || year % 400 == 0;
    return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
}

/**
 * 返回一个完整年的天数
 * 闰年366天，平年365天
 * @param year
 * @return
 */
int getDayNumOfYear(int year) {
    return isLeapYear(year) ? 366 : 365;
}

/**
 * Day of Week--上海交通大学
 * 隐含0001.01.01是周一，所以我们计算输入的日期与0001.01.01之间的差值天数，然后对7取模，即可知道偏移多少天。
 * @return
 */
int main() {
    int year;
    int month;
    string monthStr;
    int day;
    while (cin >> day >> monthStr >> year) {

        //确定月份
        for (int i = 0; i <= 12; ++i) {
            if (monthStr == monthTable[i]) {
                month = i;
                break;
            }
        }

        //计算距离0001.01.01的天数，0001.01.01是周一
        int dayNumber = 0;
        //年份要从0001开始，不可以从0000开始
        for (int j = 1; j < year; ++j) {
            dayNumber += getDayNumOfYear(j);
        }
        for (int k = 0; k < month; ++k) {
            dayNumber += dayTable[isLeapYear(year)][k];
        }
        dayNumber += day;

        //dayNumber%7即可
        cout << weekDayTable[dayNumber % 7] << endl;
    }
    return 0;
}