1+ public class Solution
2+ {
3+ #region Without Using Built-In Functions
4+ public static byte DayOfWeekOrder ( int day , int month , int year )
5+ {
6+ short a , y , m ;
7+ a = ( short ) ( ( 14 - month ) / 12 ) ;
8+ y = ( short ) ( year - a ) ;
9+ m = ( short ) ( month + ( 12 * a ) - 2 ) ;
10+ // Gregorian://0:sun, 1:Mon, 2:Tue...etc
11+ return ( byte ) ( ( day + y + ( y / 4 ) - ( y / 100 ) + ( y / 400 ) + ( ( 31 * m ) / 12 ) ) % 7 ) ;
12+ }
13+ 14+ public static string DayOfTheWeek ( int day , int month , int year )
15+ {
16+ byte dayOfWeekOrder = DayOfWeekOrder ( day , month , year ) ;
17+ 18+ string [ ] arrDayNames = [ "Sunday" , "Monday" , "Tuesday" , "Wednesday" , "Thursday" , "Friday" , "Saturday" ] ;
19+ return arrDayNames [ dayOfWeekOrder ] ;
20+ }
21+ #endregion
22+ 23+ #region Using Built-In Functions
24+ public static string DayOfTheWeek2 ( int day , int month , int year )
25+ {
26+ DateTime date = new ( year , month , day ) ;
27+ return date . DayOfWeek . ToString ( ) ;
28+ }
29+ #endregion
30+ 31+ private static void Main ( )
32+ {
33+ Console . WriteLine ( DayOfTheWeek2 ( 31 , 8 , 2019 ) ) ;
34+ 35+ Console . ReadKey ( ) ;
36+ }
37+ }
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