QuickSort Algorithm just for a exercise

[evomatteater]

Just tried creating a quick sort algorithm in c# to sort an array of integers - from a long distant memory.

Yes I could of just used the in built quicksort or better still just copied and pasted somebody elses off google.. But anyway, I have noticed at times will not sort the list entirely..

Just wondered where the problem is exactly?

Please bare in mind that it has been a long time since I wrote code, so dont be too brutal lol.

        static public int[] quickSort(int[] sortArray, int left, int right)
        {
            // if there are less than 2 elements in array or comparison no need to sort
            if ((sortArray.Length < 2) || ((right-left) < 2))
            {
                return sortArray;
            }
        
            // set random number for pivot
            Random rand = new Random();
            int pivotIndex = rand.Next(left, right);


            int l = left, r = right;
            
            while (l < r)
            {
                //leave data that is already in good in relation to index
                while (sortArray[l] < sortArray[pivotIndex])
                {
                    l++;
                }
                while (sortArray[r] > sortArray[pivotIndex])
                {
                    r--;
                }

                // swap elements
                if (sortArray[l] >= sortArray[r])
                {

                    int temp = sortArray[l];
                    sortArray[l] = sortArray[r];
                    sortArray[r] = temp;

                    //continue to seek
                    l++;
                    r--;
                }
            }

            // recursive call to sort either side of pivot
            quickSort(sortArray, left, pivotIndex);
            quickSort(sortArray, pivotIndex, right);


            return sortArray;

        }

[Peter_B]

        static public int[] quickSort(int[] sortArray, int left, int right)
        {
            // if there are less than 2 elements in array or comparison no need to sort
            if ((sortArray.Length < 2) || ((right-left) < 2))
            {
                return sortArray;
            }
        // rest of code...
        }

Suppose you call this on a two element array, so left == 0 and right == 1. Then (right-left) == 1, i.e. is less than 2. Your code will just return in this case without sorting the 2 elements.