Data commit

Task/Five-weekends/C-sharp/five-weekends-1.cs

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+using System;
+
+namespace _5_Weekends
+{
+    class Program
+    {
+        const int FIRST_YEAR = 1900;
+        const int LAST_YEAR = 2100;
+        static int[] _31_MONTHS = { 1, 3, 5, 7, 8, 10, 12 };
+
+        static void Main(string[] args)
+        {
+            int totalNum = 0;
+            int totalNo5Weekends = 0;
+
+            for (int year = FIRST_YEAR; year <= LAST_YEAR; year++)
+            {
+                bool has5Weekends = false;
+
+                foreach (int month in _31_MONTHS)
+                {
+                    DateTime firstDay = new DateTime(year, month, 1);
+                    if (firstDay.DayOfWeek == DayOfWeek.Friday)
+                    {
+                        totalNum++;
+                        has5Weekends = true;
+                        Console.WriteLine(firstDay.ToString("yyyy - MMMM"));
+                    }
+                }
+
+                if (!has5Weekends) totalNo5Weekends++;
+            }
+            Console.WriteLine("Total 5-weekend months between {0} and {1}: {2}", FIRST_YEAR, LAST_YEAR, totalNum);
+            Console.WriteLine("Total number of years with no 5-weekend months {0}", totalNo5Weekends);
+        }
+    }
+}

Task/Five-weekends/C-sharp/five-weekends-2.cs

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+using System;
+using System.Linq;
+using System.Collections.Generic;
+
+public class Program
+{
+    public static void Main()
+    {
+        const int startYear = 1900, endYear = 2100;
+
+        var query = (
+            from year in startYear.To(endYear)
+            from month in 1.To(12)
+            where DateTime.DaysInMonth(year, month) == 31
+            select new DateTime(year, month, 1) into date
+            where date.DayOfWeek == DayOfWeek.Friday
+            select date)
+            .ToList();
+
+        Console.WriteLine("Count: " + query.Count);
+        Console.WriteLine();
+        Console.WriteLine("First and last 5:");
+        for (int i = 0; i < 5; i++)
+            Console.WriteLine(query[i].ToString("MMMM yyyy"));
+        Console.WriteLine("...");
+        for (int i = query.Count - 5; i < query.Count; i++)
+            Console.WriteLine(query[i].ToString("MMMM yyyy"));
+        Console.WriteLine();
+        Console.WriteLine("Years without 5 weekends:");
+        Console.WriteLine(string.Join(" ", startYear.To(endYear).Except(query.Select(dt => dt.Year))));
+    }
+}
+
+public static class IntExtensions
+{
+    public static IEnumerable<int> To(this int start, int end) => Enumerable.Range(start, end - start + 1);
+}