查找离今天最近的经常性日期 - C#

Question

听起来像是作业？不,这不对.我为此制定了逻辑,但是当日期跨越多年时,我并没有这样的表现.基本上这是它应该如何工作,

StartDate: 1/1/2012

FinishDate: 1/10/2012 

RecurringInterval: 2 ( In days)

输出将是:

1/6/2012if Todays date(Date.Now)是1/5/2012(假设格式MM/dd/yyyy).达到完成日期后,检查将结束.如果在给定时间段内没有匹配日期,则必须返回今天的日期.死简单但不高效.

这有什么问题？

if (!_isRecurring)
    return DateTime.UtcNow;
DateTime initialDate = _startDate;
DateTime finalDate = _finishDate;
int recurringDays = _recurringInteral;
/*
 * start Date + recurring interval falls between start date and finishdate then get its date
 */
do
{
    //add recurring day to start date
    initialDate = initialDate.AddDays(recurringDays);
    //check if it falls in between start days and end days
     if(initialDate  <= finalDate)
    break;            
} while (initialDate <= finalDate);
//return the first occurance of the recurring day
return initialDate;

Answer 1

一个小算术应该节省一天(双关语):

var start = new DateTime(2012, 1, 1);
var end = new DateTime(2012, 10, 1);
var interval = 2; // days

var today = DateTime.Today;
var diff = (int)((today - start).TotalDays);
var mod = diff % interval;
var correction = TimeSpan.FromDays((mod > interval / 2 ? interval : 0) - mod);
var result = today + correction > end ? today : today + correction;
Console.Out.WriteLine("Result is: {0}", result);

看到它在行动.

这样做的是计算今天距离"复发点"多少天(变量mod).这显然是一个数字> = 0和<interval.如果它是间隔的一半或更小,则意味着最接近的复发点早于今天,在这种情况下mod从今天减去天数以找到该点.如果它大于间隔的一半,则意味着我们需要添加interval - mod天数来找到该点(将来会是这样).