(C#)快速排序 Quicksort

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Algorithms
{
    public class Sort
    {
        public static void QuickSort(int[] arr)
        {
            if (arr == null)
            {
                throw new ArgumentNullException("arr");
            }
            else
            {
                Partition(arr, 0, arr.Length - 1);
            }
        }

        private static void Partition(int[] arr, int left, int right)
        {
            if (left < right)
            {
                int p = left;
                Console.WriteLine("Pivot is {0}", arr[p]);
                int i = left + 1;
                int j = right;
                while (i <= j)
                {
                    while (i <= right && arr[i] <= arr[p])
                    {
                        i++;
                    }
                    while (j > left && arr[j] >= arr[p])
                    {
                        j--;
                    }
                    if (i < j)
                    {
                        Swap(arr, i++, j--);
                    }
                }
                Swap(arr, left, j);
                p = j;
                PrintData(arr);
                Partition(arr, left, p - 1);
                Partition(arr, p + 1, right);
            }
        }

        private static void Swap(int[] arr, int left, int right)
        {
            Console.WriteLine("Swap {0} with {1}", arr[left], arr[right]);
            int tmp = arr[left];
            arr[left] = arr[right];
            arr[right] = tmp;
        }

        public static int[] GenerateRandomIntArray(int length)
        {
            if (length < 0)
            {
                throw new ArgumentOutOfRangeException("length");
            }
            else if (length == 0)
            {
                return new int[] { };
            }
            else
            {
                Random random = new Random(DateTime.Now.Millisecond / 10);
                int[] arr = new int[length];
                for (int i = 0; i < length; i++)
                {
                    arr[i] = random.Next(-100, 99);
                }
                return arr;
            }
        }

        public static void PrintData(IEnumerable<int> ienum)
        {
            foreach (var item in ienum)
            {
                Console.Write(item + " ");
            }
            Console.WriteLine();
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            int[] arr = Sort.GenerateRandomIntArray(20);
            Sort.PrintData(arr);
            Sort.QuickSort(arr);
            Sort.PrintData(arr);
        }
    }
}