int[] nums = { 23, 300, 2400, 2300, 100, 1, 10, 20, 15 };

QuickSort(nums, 0, nums.Length - 1);

Console.WriteLine(String.Join(",", nums));

void QuickSort(int[] nums, int low, int high)
{
    if(low < high)
    {
        int pivot = Partition(nums, low, high);
        QuickSort(nums, low, pivot - 1);
        QuickSort(nums, pivot + 1, high);

    }
}

int Partition(int[] nums, int low, int high)
{
    int i = low - 1;
    int pivot = nums[high];

    for(int j = low; j < high; j++)
    {
        if(nums[j] < pivot)
        {
            Swap(nums, j, ++i);
        }
    }

    Swap(nums, high, ++i);

    return i;
}

void Swap(int[] nums, int j, int i)
{
    int tmp = nums[j];
    nums[j] = nums[i];
    nums[i] = tmp;
}