c# - 时间跨度的总和差异，按每年的旅行天数排序

Question

所以我有所有这些旅行日期，起始日期和截止日期。我想把所有的旅行天数加起来，然后按年份排序。但是，如果一次旅行跨越两年，我的代码将达到错误的总和:-(

给定

From date   To date      Number of days
01.01.2001  01.02.2001   32
01.01.2002  01.02.2002   32
01.05.2002  01.08.2002   93
20.12.2002  01.03.2003   72
01.02.2009  01.02.2010   366
01.01.2013  02.02.2015   763

                   Sum   1358

我的代码产生了这个。然而，它犯了一个错误:

Year    Total days
2001    32
2002    137
2003    60
2009    334
2010    32
2013    365
2014    398        <---- here is a case where my code is wrong

Sum     1358

代码

var dates = new Dictionary<int, int>();
var stays = GetStays();
var returnString = "Year, Total days<br><br>";
foreach (var stay in stays)
{
    var totalTravelDays = stay.ToDate.Value.AddDays(1) - stay.FromDate;

    var currentYear = stay.FromDate.Value.Year;
    var nextYear = stay.FromDate.Value.AddYears(1).Year;
    var nextYearDate = new DateTime(stay.FromDate.Value.Year, 1, 1).AddYears(1);

    var daysInThisYear = new TimeSpan?();
    var daysInNextYear = new TimeSpan?();

    if (stay.FromDate.Value.Year != stay.ToDate.Value.Year)
    {
        daysInThisYear = nextYearDate - stay.FromDate;
        daysInNextYear = totalTravelDays - daysInThisYear;
    }
    else
    {
        daysInThisYear = totalTravelDays;
        daysInNextYear = new TimeSpan(0);
    }

    if (dates.ContainsKey(currentYear))
        dates[currentYear] += daysInThisYear.Value.Days;
    else
        dates[currentYear] = daysInThisYear.Value.Days;

    if (dates.ContainsKey(nextYear))
        dates[nextYear] += daysInNextYear.Value.Days;
    else
        dates[nextYear] = daysInNextYear.Value.Days;
}

感谢帮助:)

Answer 1

假设var stays = List<Stay>(); ，你可以试试这个:

var days = stays.SelectMany(s =>
        Enumerable
            .Range(0, (s.ToDate - s.FromDate).Days + 1)
            .Select(d => s.FromDate.AddDays(d)))
    .GroupBy(d => d.Year)
    .Select(s => new { Year = s.Key, TotalDays = s.Count() })
    .ToList();

days.ForEach(d =>
{
    Console.WriteLine("{0} {1}", d.Year, d.TotalDays);
});

上面的输出是:

2001 32
2002 137
2003 60
2009 334
2010 32
2013 365
2014 365
2015 33