LeetCode—— 1185 一周中的第几天

问题描述

给你一个日期，请你设计一个算法来判断它是对应一周中的哪一天。

输入为三个整数：day、month 和 year，分别表示日、月、年。

您返回的结果必须是这几个值中的一个 {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}。

示例 1：
输入：day = 31, month = 8, year = 2019
输出："Saturday"示例 2：
输入：day = 18, month = 7, year = 1999
输出："Sunday"示例 3：
输入：day = 15, month = 8, year = 1993
输出："Sunday"提示：给出的日期一定是在 1971 到 2100 年之间的有效日期。

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/day-of-the-week
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

执行结果

代码描述

思路之一：找现有函数。——来自解题报告

#include<time.h>
class Solution {
public:    string dayOfTheWeek(int day, int month, int year) {//1970/1/1  thursdaychar *weeknames[] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};tm now = {.tm_mday = day,.tm_mon = month - 1,.tm_year = year - 1900};mktime(&now);return weeknames[now.tm_wday];}
};

思路之二：知道起始那天是周几，然后对7取余计算当前是周几。——来自解题报告

class Solution {
public:string dayOfTheWeek(int day, int month, int year) {//1970/1/1  thursdaychar *weeknames[] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};int mday[]={31,28,31,30,31,30,31,31,30,31,30,31};int wday = 4;int i = 0;for (i=1970; i<year; i++){if((i%4==0 && i%100!=0) || i%400==0){wday += (366%7);}else{wday += (365%7);}}if((i%4==0 && i%100!=0) || i%400==0){mday[1]++;}wday %= 7;for(i=1; i<month; i++){wday += mday[i-1] % 7;}wday += day-1;wday %= 7;return string(weeknames[wday]);}
};