日期时间代码怎么写（和日期相关的代码和bug——一道力扣题中的小发现）
目录
Day of the Week
题目大意
常规方法
Python代码
Golang代码
C++代码
基姆拉尔森公式
Python代码
Golang代码
C++代码
使用库函数
Python代码
Golang代码
C++代码
Day of the Week
Given a date, return the corresponding day of the week for that date.
The input is given as three integers representing the day , month and year respectively.
Return the answer as one of the following values {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"} .Example 1:
Input: day = 31, month = 8, year = 2019
Output: "Saturday"
Example 2:
Input: day = 18, month = 7, year = 1999
Output: "Sunday"
Example 3:
Input: day = 15, month = 8, year = 1993
Output: "Sunday"题目大意
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"} 。
提示：
给出的日期一定是在 1971 到 2100 年之间的有效日期 。
解题思路：
给出一个日期 ，要求算出这一天是星期几 。常规方法
从1971.1.1起 ，先累计整年year 、整月month-1的天数 ，再加上最后一个月month的天数day ，然后总天数减1后与7求余 。最后得到的余数在星期字串数组中位置索引 ，显然前提要知道1971.1.1这个基准日期是星期几 ，再作一个索引位移就是答案 。
另外常规方法还需要判断year是否闰年 ，规则：y%4==0 and y%100!=0 or y%400==0 ，据说是1582
Python代码
python代码非常简单 ，不需另外导入库只用内置函数就能搞定 。
class Solution(object): def DayOfWeek(self, year, month, day): days = 0 isLeapYear = lambda y:y%4==0 and y%100!=0 or y%400==0 monthday = [31,28,31,30,31,30,31,31,30,31,30,31] week = ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"] monthday[1] = 29 if isLeapYear(year) else 28 for i in range(1971,year): days += 366 if isLeapYear(i) else 365 days += sum(monthday[:month-1], day-1) return week[(days+5)%7] if __name__ == "__main__": s = Solution() print(s.DayOfWeek(2019,8,31)) print(s.DayOfWeek(1999,7,18)) print(s.DayOfWeek(1993,8,15)) print(s.DayOfWeek(1971,6,12)) print(s.DayOfWeek(2023,2,22)) print(s.DayOfWeek(2040,6,13))输出：
Saturday
Sunday
Sunday
Saturday
Wednesday
WednesdayGolang代码
基本原理相同 ，另外自定义一个数组求和公式即可 。
package main import "fmt" func DayOfWeek(year int, month int, day int) string { days := 0 isLeapYear := func(y int) bool { return y%4 == 0 && y%100 != 0 || y%400 == 0 } Sum := func(nums []int, initNum int) int { var sumNum int = 0 for _, num := range nums { sumNum += num } return sumNum + initNum } monthday := []int{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31} week := []string{"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"} if isLeapYear(year) { monthday[1] = 29 } else { monthday[1] = 28 } for i := 1971; i < year; i++ { if isLeapYear(i) { days += 366 } else { days += 365 } } days += Sum(monthday[:month-1], day-1) return week[(days+5)%7] } func main() { fmt.Println(DayOfWeek(2019, 8, 31)) fmt.Println(DayOfWeek(1999, 7, 18)) fmt.Println(DayOfWeek(1993, 8, 15)) fmt.Println(DayOfWeek(1971, 6, 12)) fmt.Println(DayOfWeek(2023, 2, 22)) fmt.Println(DayOfWeek(2040, 6, 13)) }输出：
Saturday
Sunday
Sunday
Saturday
Wednesday
Wednesday
成功: 进程退出代码 0.
C++代码
引入C++11的容器vector ，可以省掉最后一个非整年的各月份日数循环累加 ，只要用<numeric>库中的函数accumulate ，方便累加非整年的各月份日数 ，并且把day作为基准数一并累加掉 。
#include<iostream> #include<vector> #include<numeric> using namespace std; class Solution { public: string DayOfWeek(int year, int month, int day) { int days = 0; auto isLeapYear = [](int y) { return y%4==0 && y%100!=0 || y%400==0; }; vector<int> monthday = {31,28,31,30,31,30,31,31,30,31,30,31}; vector<string> week = {"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"}; monthday[1] = isLeapYear(year) ? 29 : 28; for (int i=1971;i<year;i++) days += isLeapYear(i) ? 366 : 365; days += accumulate(monthday.begin(), monthday.begin()+month-1, day-1); return week[(days+5)%7]; } }; int main() { Solution s; cout << s.DayOfWeek(2019,8,31) << endl; cout << s.DayOfWeek(1999,7,18) << endl; cout << s.DayOfWeek(1993,8,15) << endl; cout << s.DayOfWeek(1971,6,12) << endl; cout << s.DayOfWeek(2023,2,22) << endl; cout << s.DayOfWeek(2040,6,13) << endl; return 0; }Dev C++ 6.3 编译通过：
Saturday
Sunday
Sunday
Saturday
Wednesday
Wednesday--------------------------------
Process exited after 0.02175 seconds with return value 0
请按任意键继续. . .基姆拉尔森公式
万能的日期计算公式 ，不用知道基准日是哪一天 ，也不需要判断year是否为闰年 。
公式：weekday = (day+2month+3(month+1)/5+year+year/4-year/100+year/400+1)%7
注意：1月和2月需看做上一年的13月与14月 ，即 month<3时 ， year-=1; month+=12
Python代码
class Solution(object): def DayOfWeek(self, year, month, day): week = ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"] if month<3: year, month = year-1, month+12 weekday = (day+2*month+3*(month+1)//5+year+year//4-year//100+year//400+1)%7 return dict(zip(range(7),week)).get(weekday) if __name__ == "__main__": s = Solution() print(s.DayOfWeek(2019,8,31)) print(s.DayOfWeek(1999,7,18)) print(s.DayOfWeek(1993,8,15)) print(s.DayOfWeek(1971,6,12)) print(s.DayOfWeek(2023,2,22)) print(s.DayOfWeek(2040,6,13))Golang代码
package main import "fmt" func DayOfWeek(year int, month int, day int) string { week := []string{"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"} if month < 3 { year -= 1 month += 12 } weekday := (day + 2*month + 3*(month+1)/5 + year + year/4 - year/100 + year/400 + 1) % 7 return week[weekday] } func main() { fmt.Println(DayOfWeek(2019, 8, 31)) fmt.Println(DayOfWeek(1999, 7, 18)) fmt.Println(DayOfWeek(1993, 8, 15)) fmt.Println(DayOfWeek(1971, 6, 12)) fmt.Println(DayOfWeek(2023, 2, 22)) fmt.Println(DayOfWeek(2040, 6, 13)) }C++代码
#include<iostream> using namespace std; class Solution { public: string DayOfWeek(int year, int month, int day) { const char *week[7] = {"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"}; if (month < 3) { year -= 1; month += 12; } int weekday = (day+2*month+3*(month+1)/5+year+year/4-year/100+year/400+1)%7; return week[weekday]; } }; int main() { Solution s; cout << s.DayOfWeek(2019,8,31) << endl; cout << s.DayOfWeek(1999,7,18) << endl; cout << s.DayOfWeek(1993,8,15) << endl; cout << s.DayOfWeek(1971,6,12) << endl; cout << s.DayOfWeek(2023,2,22) << endl; cout << s.DayOfWeek(2040,6,13) << endl; return 0; }使用库函数
Python代码
datetime库
import datetime class Solution(object): def DayOfWeek(self, year, month, day): week = ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"] weekday = datetime.date(year,month,day).isoweekday() return week[weekday%7] if __name__ == "__main__": s = Solution() print(s.DayOfWeek(2019,8,31)) print(s.DayOfWeek(1999,7,18)) print(s.DayOfWeek(1993,8,15)) print(s.DayOfWeek(1971,6,12)) print(s.DayOfWeek(2023,2,22)) print(s.DayOfWeek(2040,6,13))calendar库
import calendar class Solution(object): def DayOfWeek(self, year, month, day): week = ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"] weekday = calendar.weekday(year,month,day)+1 return week[weekday%7] if __name__ == "__main__": s = Solution() print(s.DayOfWeek(2019,8,31)) print(s.DayOfWeek(1999,7,18)) print(s.DayOfWeek(1993,8,15)) print(s.DayOfWeek(1971,6,12)) print(s.DayOfWeek(2023,2,22)) print(s.DayOfWeek(2040,6,13))Golang代码
time库 ，超级省事 ，连星期数组都不用了 。
package main import ( "fmt" "time" ) func DayOfWeek(year int, month int, day int) string { return time.Date(year, time.Month(month), day, 0, 0, 0, 0, time.Local).Weekday().String() } func main() { fmt.Println(DayOfWeek(2019, 8, 31)) fmt.Println(DayOfWeek(1999, 7, 18)) fmt.Println(DayOfWeek(1993, 8, 15)) fmt.Println(DayOfWeek(1971, 6, 12)) fmt.Println(DayOfWeek(2023, 2, 22)) fmt.Println(DayOfWeek(2040, 6, 13)) }C++代码
ctime库
#include<iostream> #include<ctime> using namespace std; class Solution { public: string DayOfWeek(int year, int month, int day) { const char *week[7] = {"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"}; struct tm t = {0}; t.tm_year = year - 1900; t.tm_mon = month - 1; t.tm_mday = day; mktime(&t); return week[t.tm_wday%7]; } }; int main() { Solution s; cout << s.DayOfWeek(2019,8,31) << endl; cout << s.DayOfWeek(1999,7,18) << endl; cout << s.DayOfWeek(1993,8,15) << endl; cout << s.DayOfWeek(1971,6,12) << endl; cout << s.DayOfWeek(2023,2,22) << endl; cout << s.DayOfWeek(2040,6,13) << endl; return 0; }输出：
Saturday
Sunday
Sunday
Saturday
Wednesday
Sunday--------------------------------
Process exited after 0.02402 seconds with return value 0
请按任意键继续. . .发现没？ 2040.6.13返回的星期是错的！
网上查了资料 ，原来ctime库的CTime对象是有指定范围的：
static CTime WINAPI GetCurrentTime( );
获取系统当前日期和时间 。返回表示当前日期和时间的CTime对象 。
int GetYear( ) const；
获取CTime对象表示时间的年份 。范围从1970年1月1日到2038年1月18日 。
时间范围测试：
#include<iostream> #include<ctime> using namespace std; class Solution { public: string DayOfWeek(int year, int month, int day) { const char *week[7] = {"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"}; struct tm t = {0}; t.tm_year = year - 1900; t.tm_mon = month - 1; t.tm_mday = day; mktime(&t); return week[t.tm_wday%7]; } }; int main() { Solution s; for (int i=16;i<25;i++) cout << i << ":" << s.DayOfWeek(2038,1,i) << endl; return 0; }测试结果：
16:Saturday
17:Sunday
18:Monday
19:Tuesday
20:Sunday
21:Sunday
22:Sunday
23:Sunday
24:Sunday--------------------------------
Process exited after 0.05159 seconds with return value 0
请按任意键继续. . .2038.1.19日的星期也对 ，之后的全部返回Sunday 。
修改这个问题 ，技术上一点问题都没有 。 目前C++都发展到C++20了 ，而我用的是C++11 ，暂不知道之后版本的库文件有没有对此问题作过更新 。那么 ，问题来了：
之前用C语言写的的软件 ，用ctime或者time.h获取时间的软件在2038年1月19日之后都会发生错误 。还好 ，还有整整15年时间来改正这个“时间Bug ” 。
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