Handy Non-recursive way to find the contiguous natural number ranges given a list of numbers. For example: A list of numbers 1,2,3,6,7,8,9,14,15,22 the contiguous ranges would be: 1-3, 6-9, 14-15, 22-22 Potential issues: since it finds all the missing Numbers, ranges with huge gaps of missing numbers can hinder performance.

FindRanges.cs

public List<Range> findRanges(List<int> numbers) {
            List<Range> ranges = new List<Range>(); // create a list of ranges that will eventually be populated.
            numbers = numbers.OrderBy(x=>x).ToList<int>(); // order the list of numbers coming in.
            int min = numbers.Min(); // get the smallest number
            int max = numbers.Max(); // get the largest number
            List<int> missingNumbers = new List<int>(); // create an empty list of missing numbers
            int i = min; // create a counter for stepping through all the numbers starting with the smallest number
            while (i < max) { // step through each possible number from min to max.
                if (!numbers.Contains(i)) { // if the number doesnt exist from our list, its a missing number
                    // found a gap in the number (missing number)
                    missingNumbers.Add(i); // add the number to the list of missing numbers.
                }
                i++; // increase the counter by 1.
            }
            int tempLow = min; // create a tempLow starting with the min since its our first low value.
            int countInc = 1; // create a count incrementer. This is for checking for the last possible range. last found number to max.
            foreach (int num in missingNumbers) { // step through the list of missing numbers
                if (tempLow != num) { // if tempLow is not the same as the missing number create a new range
                    Range r = new Range { // new rang is always the tempLow to the missing number - 1
                        low = tempLow, // temp low which is the first valid number after the last high value
                        high = num - 1 // last high value is the last valid number before the current missing number
                    };
                    // example 1,2,5,6 - 3,4 are both missing numbers. one less than missing number is a high number and the low number was the last valid high number
                    tempLow = num + 1; // add 1 to the last misisng number in attempt to find the next lowest number- note will not be used if its a missing number with the if statement above.
                    ranges.Add(r); // add the range to the list of ranges.
                } else { // if tempLow is accidentally set to a missing number, increase it by 1 until is not a missing number
                    tempLow += 1; // tempLow should be increase until it is a valid number ( not a missing number)
                }
                if (missingNumbers.Count == countInc) { // if this is the last item in the foreach of missing numbers ( then create the last range
                    Range lastRange = new Range{
                        low = tempLow, // last valid number
                        high = max // the last and highest value
                    };
                    if(!ranges.Contains(lastRange)){ // if the last valid number has not been added to the ranges, do so. 
                        ranges.Add(lastRange);
                    }
                }
                    countInc += 1; // increase the foreach counter by 1.
            }
            return ranges; // return the list of ranges.
        }

RangeClass.cs

    public class Range {
        public int low { get; set; } // low value for the range
        public int high { get; set; } // high value for the range
    }