1+ public class Solution
2+ {
3+ #region Without Using Built-In Functions
4+ public static bool IsLeapYear ( short year )
5+ => ( year % 400 == 0 ) || ( year % 4 == 0 && year % 100 != 0 ) ;
6+ 7+ public static byte DaysInMonth ( short year , byte month )
8+ {
9+ if ( month < 1 || month > 12 )
10+ {
11+ return 0 ;
12+ }
13+ 14+ byte [ ] daysInMonth = { 0 , 31 , 28 , 31 , 30 , 31 , 30 , 31 , 31 , 30 , 31 , 30 , 31 } ;
15+ 16+ return ( month == 2 ) ? ( byte ) ( IsLeapYear ( year ) ? 29 : 28 ) : ( daysInMonth [ month ] ) ;
17+ }
18+ 19+ public static int DayOfYear ( string date )
20+ {
21+ if ( ! DateTime . TryParse ( date , out DateTime dateObject ) )
22+ {
23+ return - 1 ;
24+ }
25+ 26+ int totalDays = 0 ;
27+ 28+ for ( byte i = 1 ; i < dateObject . Month ; i ++ )
29+ {
30+ totalDays += DaysInMonth ( ( short ) dateObject . Year , i ) ;
31+ }
32+ 33+ return ( totalDays + dateObject . Day ) ;
34+ }
35+ #endregion
36+ 37+ #region Using Built-In Functions
38+ public static int DayOfYear2 ( string date )
39+ {
40+ if ( ! DateTime . TryParse ( date , out DateTime dateObject ) )
41+ {
42+ return - 1 ;
43+ }
44+ 45+ return dateObject . DayOfYear ;
46+ }
47+ #endregion
48+ 49+ private static void Main ( )
50+ {
51+ Console . WriteLine ( DayOfYear ( "2019年02月10日" ) ) ;
52+ Console . ReadKey ( ) ;
53+ }
54+ }
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