Iterate through a list of dates with a known interval and create list with inverse dates in vb.net? - vb.net

Question

I'm trying to use a list of dates/times with a known interval of 10 minutes to create a list of all inverse times. I need to block off calendar times that are not available; but i only know what calendar times are available to start. My list of available slots needs to populate a calendar by blocking off all of the time that the user is not available. Each of the available appointments from my endpoint is a 10 minute interval.
Input Data Set:
6/7/19 - 8:00
6/7/19 - 8:20
6/7/19 - 9:30
6/7/19 - 10:10
6/7/19 - 11:20
With the known 10 minute interval, this means 8:00 - 8:10 is available, and should not be in my resulting list. I also block from day start 00:00 until first opening, and from last appointment, until end of day.
Expected Output:
6/7/19 - 0:00,8:00
6/7/19 - 8:10,8:20
6/7/19 - 8:30,9:30
6/7/19 - 9:40,10:10
6/7/19 - 10:20,11:20
6/7/19 - 11:30,24:59
My current code:
'// Setup some test data
Dim DateList As New List(Of DateTime)
DateList.Add(New DateTime(2019, 6, 7, 8, 0, 0))
DateList.Add(New DateTime(2019, 6, 7, 8, 20, 0))
DateList.Add(New DateTime(2019, 6, 7, 9, 30, 0))
DateList.Add(New DateTime(2019, 6, 7, 10, 10, 0))
DateList.Add(New DateTime(2019, 6, 7, 11, 20, 0))
Dim DateTemplate As New List(Of Tuple(Of DateTime, DateTime))
'// Calculate starting offset
DateTemplate.Add(Tuple.Create(New DateTime(2019, 6, 7, 0, 0, 0), DateList.First.AddMinutes(0)))
'// Loop through items
For idx = 0 To (DateList.Count - 2)
DateTemplate.Add(Tuple.Create(DateList(idx).AddMinutes(10), DateList(idx + 1).AddMinutes(0)))
Next
'// Calculate ending offset
DateTemplate.Add(Tuple.Create(DateList.Last.AddMinutes(10), New DateTime(2019, 6, 7, 23, 59, 0)))
For Each i In DateTemplate '// Show to console to debug
Console.WriteLine(i.Item1.ToString & " - " & i.Item2.ToString)
Next

Answer 1

If you split your day up in 10 minute intervals you know that there will be 144 slots (60 minutes / 10 intervals * 24 hours). With that being said, the way that I would tackle this problem would be to create a Dictionary where the key would represent the Date and the value would be a String array.
The values in the String array would be an Empty string to represent an open time slot or populated to represent an existing appointment.
You could then calculate the Date and Time by getting the outer Dictionary's key and the time by multiplying the index of the String in relation to the array by 10.
Take a look at this example:
Dim DateTemplate As New Dictionary(Of Date, String())
For Each existingAppointment As DateTime In DateList
If Not DateTemplate.ContainsKey(existingAppointment.Date) Then
DateTemplate.Add(existingAppointment.Date, Enumerable.Range(1, 144).Select(function(i) String.Empty).ToArray())
End If
DateTemplate(existingAppointment.Date)(existingAppointment.TimeOfDay.TotalMinutes \ 10) = "Apointment Booked"
Next
Live Demo: https://dotnetfiddle.net/FygG54