title: Python "Meeting Finder" algorithm giving wrong output
body: <p>Im working on an application in python that finds free days in given bounds, with given persons times in which they aren't free. It works by creating a list of possible days and then removing the days in which the perons aren't free. But depending on the boundaries given it puts our wrong &quot;free days&quot;, when the bounds are 1 to 30 (or 31 bc the day 30 is included) it works, but when the bounds are i.e. 4 to 33 (or 34 bc the day 33 is included), wrong days are calculated. The code:</p>
  <pre><code>person_1 = ['4-16', '18-24']
  person_2 = ['2-14', '17-25']
  person_3 = ['6-8', '12-20']
  person_4 = ['10-22']
  allPeople = [person_1, person_2, person_3, person_4]
  
  startDaySlot = 1
  endDaySlot = 31
  allTimeSlots = list(range(startDaySlot, endDaySlot))
  commonFreeSlots = []
  
  for i in allPeople:
      for l in i:
          startSlot, endSlot = l.split('-')
          print(startSlot + '-' + endSlot)
          del allTimeSlots[int(startSlot) - 1:int(endSlot)]
          print(str(allTimeSlots))
  
  print(str(allTimeSlots))
  </code></pre>
  <p>I recommend trying the code yourself with different boundaries.</p>