快速排序——算法系列

快速排序：

思想：主要是利用了分而治之的思想，将一个大的排序问题简化成一个一个小的问题。

代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Net;
using System.Threading;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            for (int i = 1; i <= 5; i++)
            {
                List<int> list = new List<int>();
                //插入2k个随机数到数组中
                for (int j = 0; j < 2000; j++)
                {
                    Thread.Sleep(1);
                    list.Add(new Random((int)DateTime.Now.Ticks).Next(0, 100000));
                }
                Console.WriteLine("\n第" + i + "次比较：");
                Stopwatch watch = new Stopwatch();
                watch.Start();
                var result = list.OrderBy(single => single).ToList();//这里这个single=>single不懂
                watch.Stop();
                Console.WriteLine("\n系统的快速排序耗费时间：" + watch.ElapsedMilliseconds);
                Console.WriteLine("输出前是十个数："+string.Join(",",result.Take(10).ToList()));
                watch.Start();
                new QuickSortClass().QuickSort(list, 0, list.Count - 1);
                watch.Stop();
                Console.WriteLine("\n自己的快速排序耗费时间：" + watch.ElapsedMilliseconds);
                Console.WriteLine("输出前是十个数：" + string.Join(",", result.Take(10).ToList()));//这里也不是很懂
                
            }
            Console.ReadLine();
        }
        //快速排序算法
    }
    public class QuickSortClass
    {
        private int Division(List<int> list, int left, int right)
        {
            int baseNum = list[left];
            while (left < right)
            {
                while (left < right && baseNum <= list[right])
                    right--;
                list[left] = list[right];
                while (left < right && baseNum >= list[left])
                    left++;
                list[right] = list[left];
            }
            list[left] = baseNum;
            return left;
        }

        public void QuickSort(List<int> list, int left, int right)
        {
            if (left < right)
            {
                int i = Division(list, left, right);
                QuickSort(list, left, i - 1);
                QuickSort(list, i + 1, right);
            }
        }
    }
}

总结：

快速排序是排序算法中最快的算法了，快的程度令人发指。

http://www.cnblogs.com/huangxincheng/archive/2011/11/14/2249046.html