二分查找（折半查找）

namespace BinarySearch.CSharp
{
    class Program
    {
        static void Main(string[] args)
        {
            List<int> list = new List<int> { 10,20,30,40,50,60,70,80,90 };

            Console.WriteLine("********************二分查找********************\n");
            Display(list);
            int result = BinarySearch(list, 40);
            if (result != -1) Console.WriteLine("40在列表中的位置是:{0}", result);
            else Console.WriteLine("对不起，列表中不存在该元素!");

            Console.ReadKey();
        }

        /// <summary>
        /// 二分查找
        /// </summary>
        /// <param name="list">查找表</param>
        /// <param name="key">给定值</param>
        /// <returns>给定值在列表中的位置</returns>
        public static int BinarySearch(List<int> list, int key)
        {
            int low = 0;
            int high = list.Count - 1;

            while (low <= high)
            {
                int middle = (low + high) / 2;

                //判断中间记录是否与给定值相等
                if (list[middle] == key)
                {
                    return middle;
                }
                else
                {
                    //在中间记录的左半区查找
                    if (list[middle] > key) high = middle - 1;

                    //在中间记录的右半区查找
                    else low = middle + 1;
                }
            }

            //没有找到(查找失败)
            return -1;
        }

        private static void Display(IList<int> list)
        {
            Console.WriteLine("\n**********展示结果**********\n");

            if (list != null && list.Count > 0)
            {
                foreach (var item in list)
                {
                    Console.Write("{0} ", item);
                }
            }
            Console.WriteLine("\n**********展示完毕**********\n");
        }
    }
}