Question

EXAMPLE :if i add a range {1,10}
and another range{15,20}
i should get a message saying the ranges from 11 to 14 are missing.

Answer 1

How are you adding the ranges?

If the ranges are added in order, you can just keep the end of the last range and compare to the start of the range that you add.

If you can add the ranges in any order, you have to do the check when all ranges are added. Sort the ranges on the range start, then loop through the ranges and compare the end of a range with the start of the next range.

update

Example of the second case. First a class to hold ranges:

public class Range {

  public int From { get; private set; }
  public int To { get; private set; }

  public Range(int from, int to) {
    From = from;
    To = to;
  }

}

Create a list of ranges:

List<Range> ranges = new List<Range>();
ranges.Add(new Range(15, 20));
ranges.Add(new Range(1, 10));

Test the ranges:

ranges = ranges.OrderBy(r => r.From).ToList();
for (int i = 1; i < ranges.Count; i++) {
  int to = ranges[i - 1].To;
  int from = ranges[i].From;
  int diff = to.CompareTo(from - 1);
  if (diff < 0) {
    Response.Write("Range from " + (to + 1).ToString() + " to " + (from - 1).ToString() + " is missing<br/>");
  } else if (diff > 0) {
    Response.Write("Range ending at " + to.ToString() + " overlaps range starting at " + from.ToString() + "<br/>");
  }
}

Note: The code checks for both gaps in the ranges and overlapping ranges. If overlapping ranges is not a problem, just remove the part that checks for diff > 0.