C#实现折半查找（递归，非递归）

源文件：http://pan.baidu.com/share/link?shareid=439727&uk=3912660076

代码参考来源于课本：

//Main：

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

namespace BinarySearch
{
    class Program
    {
        static void Main(string[] args)
        {
            Function obj = new Function();

            int position;

            Console.WriteLine("The array is:");
            Console.WriteLine(obj);

            while (true)
            {
                Console.WriteLine("Please choose:");
                Console.WriteLine("1.BinarySerach；");
                Console.WriteLine("2.RecursiveBinarySearch；");
                Console.WriteLine("3.Exit；");

                int number = Convert.ToInt32(Console.ReadLine());
                Console.WriteLine();

                switch (number)
                {
                    case 1:
                        Console.WriteLine("Please enter an integer target value:");
                        int targetValue = Convert.ToInt32(Console.ReadLine());
                        Console.WriteLine();
                        position = obj.BinarySerach(targetValue);

                        if (position == -1)
                            Console.WriteLine("The integer {0} was not found.\n",
                               targetValue);
                        else
                            Console.Write(
                               "The integer {0} was found in position:{1}\n",
                               targetValue, position);
                        break;
                    case 2:
                        Console.WriteLine("Please enter an integer target value:");
                        int targetValue2 = Convert.ToInt32(Console.ReadLine());
                        Console.WriteLine();
                        position = obj.RecursiveBinarySearchHelp(targetValue2);

                        if (position == -1)
                            Console.WriteLine("The integer {0} was not found.\n",
                               targetValue2);
                        else
                            Console.Write(
                               "The integer {0} was found in position:{1}\n",
                               targetValue2, position);
                        break;
                    case 3:
                        Environment.Exit(0);
                        break;
                }
            }
        }
    }
}

//Class:

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

namespace BinarySearch
{
    class Function
    {
        /// <summary>
        /// 声明变量
        /// </summary>
        private int[] array;
        private static Random ran = new Random();

        /// <summary>
        ///  初始化数组
        /// </summary>
        /// <param name="length"></param>
        public Function()
        {
            int length = ran.Next(1, 38);
            array = new int[length];
            while (length > 0)
                array[--length] = ran.Next(0, 100);
            //折半查找要求数组状态为排好序的
            Array.Sort(array);
        }

        /// <summary>
        /// 折半查找：
        ///         折半查找要求数组先排好序，将数组划分为三部分左中右部分，中间只有一个元素。
        ///     第一次迭代测试数组中的中间部分，如果匹配返回位置结束，否则与中间元素比较，
        ///     若小于中间元素说明要查找的元素在数组的左边，反之在右边，确定在哪边后，放弃另一边和中间.
        ///     再把只有这边的元素划分为三部分，进行类推......直到数组只有一个元素为止。返回结果，
        /// 核心算法时间复杂度：
        ///                 T(n)=O(㏒n)
        /// </summary>
        /// <param name="targetValue"></param>
        /// <returns></returns>
        public int BinarySerach(int targetValue)
        {
            //初始假定没找到返回位置为-1；
            int position = -1;
            //
            int left, middle, right;
            //初始为划分数组中为三段
            //最左边，
            left = 0;
            //中间
            middle = array.Length / 2;
            //最右边
            right = array.Length - 1;
            do
            {//每划分一次就展示一次划分情况
                Console.Write(RemainingElements(left, right));
                for (int i = 0; i < middle; i++)
                    Console.Write("   ");
                Console.WriteLine(" * ");
                //目标元素刚好就是中间的元素返回其位置
                if (targetValue == array[middle])
                    return position = middle;
                //目标元素小于中间的元素==在数组的左边。改变划分范围最右边变为原来的左边的最右边。
                else if (targetValue < array[middle])
                    right = middle - 1;
                else
                    //目标元素大于中间的元素==在数组的右边。改变划分范围最左边变为原来的右边的最左边。
                    left = middle + 1;
                //重新初始化middle
                middle = (left + right) / 2;

            } while (left <= right);//至最后只有一个元素为止
            //返回结果
            return position;
        }

        /// <summary>
        /// 辅助代码
        /// </summary>
        /// <param name="targetValue"></param>
        /// <returns></returns>
        public int RecursiveBinarySearchHelp(int targetValue)
        {
            return RecursiveBinarySearch(0, array.Length - 1, targetValue);
        }

        /// <summary>
        /// 折半查找的递归算法
        /// </summary>
        /// <param name="left"></param>
        /// <param name="right"></param>
        /// <param name="targetValue"></param>
        /// <returns></returns>
        public int RecursiveBinarySearch(int left, int right, int targetValue)
        {
            //初始假定没找到返回位置为-1；
            int position = -1;
            //没有找到
            if (left > right)
                return position;
            //
            int middle = (left + right) / 2;
            //
            Console.Write(RemainingElements(left, right));
            for (int i = 0; i < middle; i++)
                Console.Write("   ");
            Console.WriteLine(" * ");

            //
            if (targetValue == array[middle])
                return position = middle;
            else if (targetValue < array[middle])
                position = RecursiveBinarySearch(left, middle - 1, targetValue);
            else
                position = RecursiveBinarySearch(middle + 1, right, targetValue);
            //
            return position;
        }

        /// <summary>
        /// 展示
        /// </summary>
        /// <param name="low"></param>
        /// <param name="high"></param>
        /// <returns></returns>
        public string RemainingElements(int low, int high)
        {
            string temporary = string.Empty;

            // output spaces for alignment
            for (int i = 0; i < low; i++)
                temporary += "   ";

            // output elements left in array
            for (int i = low; i <= high; i++)
                temporary += array[i] + " ";

            temporary += "\n";
            return temporary;
        } // end method RemainingElements

        // method to output values in array
        public override string ToString()
        {
            return RemainingElements(0, array.Length - 1);
        }
    }
}

//运行结果截图：