二分查找有两个条件：

1. 数组必须有序，无序数组查找之前需要先让其有序
2. 只限于顺序存储结构

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)        {            List
     
       list = new List
      
       ();            for (int i = 0; i < 2000; i++)            {                Thread.Sleep(1);                list.Add(new Random((int)DateTime.Now.Ticks).Next(0, 100));            }            list.OrderBy(single => single).ToList();            for (int i = 0; i < 100; i++)            {                Thread.Sleep(100);                if (BinarySearch(list, i) == 1)                    Console.WriteLine("找到了");                else                    Console.WriteLine("没找到");            }                        Console.ReadLine();        }        public static int BinarySearch(List
       
         list, int key)        {            int low = 0;            int high = list.Count - 1;            while (low <= high)            {                int middle = (low + high) / 2;                if (key == list[middle])                    return 1;                else if (key > list[middle])                    low = middle + 1;                else                    high = middle - 1;            }            return 0;        }    }}