c# - 这是找到给定月份每周的好算法吗？

Question

我需要用一个月(定义为开始日期和结束日期)并返回该月每周的一组日期范围。一周定义为星期日到星期六。如果您在开始栏中双击您的 Windows 日期，则一种可视化它的好方法:

2011 年 10 月有 6 周:10/1-10/1、10/2-10/8、10/9-10/15、10/16-10/22、10/23-10/29 日和 10/30-10/31。

我可以将每周描述为一个结构:

   struct Range
   {
      public DateTime Start;
      public DateTime End;

      public Range(DateTime start, DateTime end)
      {
         Start = start;
         End = end;
      }
   }

我需要编写一个函数，它需要一个月的时间并返回其中的一个范围数组。这是我的第一次尝试，它似乎有效并解决了明显的边缘情况:

public static IEnumerable<Range> GetRange(DateTime start, DateTime end)
{
   DateTime curStart = start;
   DateTime curPtr = start;
   do
   {
      if (curPtr.DayOfWeek == DayOfWeek.Saturday)
      {
         yield return new Range(curStart, curPtr);
         curStart = curPtr.AddDays(1);
      }

      curPtr = curPtr.AddDays(1);
   } while (curPtr <= end);

   if(curStart <= end)
      yield return new Range(curStart, end);
}

我想知道是否有更简洁或更明显的方法来做同样的事情。我不太关心性能，但我想提高代码的可读性并使算法更简洁一些。也许有一个非常有创意的解决方案涉及单个 LINQ 表达式或其他东西。谢谢!

Answer 1

正如 Previti 所建议的那样，这是基于简单地增加 7，以供国际使用。如果您的 C# < 4.0，请删除默认参数 = DayOfWeek.Sunday

public static IEnumerable<Range> GetRange(DateTime start, DateTime end, DayOfWeek startOfTheWeek = DayOfWeek.Sunday)
{
    if (start > end)
    {
        throw new ArgumentException();
    }

    // We "round" the dates to the beginning of the day each
    start = start.Date;
    end = end.Date;

    // The first week. It could be "shorter" than normal. We return it "manually" here
    // The 6 + startOfWeek - start.DayOfWeek will give us the number of days that you
    // have to add to complete the week. It's mod 7. It's based on the idea that 
    // the starting day of the week is a parameter.
    DateTime curDay = new DateTime(Math.Min(start.AddDays((6 + (int)startOfTheWeek - (int)start.DayOfWeek) % 7).Ticks, end.Ticks), start.Kind);

    yield return new Range(start, curDay);

    curDay = curDay.AddDays(1);

    while (curDay <= end)
    {
        // Each time we add 7 (SIX) days. This is because the difference between
        // as considered by the problem, it's only 6 * 24 hours (because the week
        // doesn't end at 23:59:59 of the last day, but at the beginning of that day)
        DateTime nextDay = new DateTime(Math.Min(curDay.AddDays(6).Ticks, end.Ticks), start.Kind);

        yield return new Range(curDay, nextDay);

        // The start of the next week
        curDay = nextDay.AddDays(1);
    }
}

一些小笔记:Math.Min没有为 DateTime 定义, 所以我通过 Ticks 来作弊的 DateTime s 并比较它们。然后我重建 DateTime .我总是使用 DateTimeKind的 start日期。

调试时yield代码，请记住通过使用 ToList 来“具体化”结果或 ToArray , 否则代码不会被执行:-)