How to gets the number of overlapping days between 2 ranges?

Question

let me explain the situation first - let's say i have 4 dates: BS, BE, PS, PE (S for start, E for end). I need to know how many days are over lapping when given those dates. for example : BE-05.01 , BS-10.01, PS-03.01, PE-07.01 the result is: 3 (05.01, 06.01 and 07.01 are overlapping)

I wrote the following code but it seems to messy and i want to check if maybe there is a simpler way to do this:

private static double GetNumOfOverLappingDays(DateTime BS, DateTime BE, DateTime PS, DateTime PE)
    {
        //case 1:
        //                  |--- B ---|
        //                  |----P ---|

        //case 2:
        //                  |--- B ---|
        //                          | --- P --- |

        //case 3:
        //                  |--- B ---|
        //          | --- P ---- |

        //case 4:
        //                  |--- B ---|
        //                     | - P - |

        //case 5:
        //                  |--- B ---|
        //              | -------- P -------- |

        double days = -1;
        bool isNotOverLap = (BS > PE) || (PS > BE);

        if (isNotOverLap == false)
        {
            //case 1
            if (BS == PS && BS == PE)
            {
                days = (PE - PS).TotalDays;
            }
            //case 2
            else if (BE > PS && BE < PE)
            {
                days = (BE - PS).TotalDays;
            }
            //case 3
            else if (BS > PS && BS < PE)
            {
                days = (PE - BS).TotalDays;
            }
            //case 4
            else if (BS < PS && BE > PE)
            {
                days = (PE - PS).TotalDays;
            }
            //case 5
            else if (BS > PS && BE < PE)
            {
                days = (BE - PS).TotalDays;
            }
        }
        return days+1;
    }

thanks in advance for any assitance,

Amit

Answer 1

Try this:

    private static double GetOverlappingDays(DateTime firstStart, DateTime firstEnd, DateTime secondStart, DateTime secondEnd)
    {
        DateTime maxStart = firstStart > secondStart ? firstStart : secondStart;
        DateTime minEnd = firstEnd < secondEnd ? firstEnd : secondEnd;
        TimeSpan interval = minEnd - maxStart;
        double returnValue = interval > TimeSpan.FromSeconds(0) ? interval.TotalDays : 0;
        return returnValue;
    }

Answer 2

Try to use for loop:

DateTime d1 = new DateTime(2013,12,1),
            d2 = new DateTime(2013,12,14),
            d3 = new DateTime(2013,12,10),
            d4 = new DateTime(2013,12,20);
int count = 0;

for (var d = d1.Date; d <= d2.Date; d = d.AddDays(1))
{
      if (d >= d3.Date && d <= d4.Date)
           count++;
}

Console.WriteLine(count);

Notice that this code gives integer value. If you need value in hours this code will not fit. Also this is not the most efficient approach, but it's simple and works ok for small ranges.