Binary Search(二元搜尋法)

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

//  二元搜尋法

//  https://blog.yslifes.com/archives/728

namespace BinarySearch

{

    class Program

    {

        private static int BinarySearch(int[] list, int SearchKey)

        {

            int left = 0;

            int right = list.Length;

            while (left <= right)

            {

                int mid = (left + right) / 2;//取中間位子當基準

                if (list[mid] == SearchKey)

                {

                    return mid;//找到的index值

                }

                else

                {

                    if (list[mid] < SearchKey)//在右邊的數列

                    {

                        left = mid + 1;

                    }

                    else//在左邊的數列

                    {

                        right = mid - 1;

                    }

                }

            }

            return -1;//找不到時

        }

        static void Main(string[] args)

        {

            int[] list = { 1, 2, 4, 6, 8, 9, 11, 12, 15, 18, 21, 24 };

            Console.WriteLine("原始數字串");

            for (int i = 0; i < list.Length; i++)

            {

                Console.Write(list[i] + " ");

            }

            Console.WriteLine("\r\n請輸入要查詢的數字:");

            int SearchKey = Convert.ToInt32(Console.ReadLine());

            int index = BinarySearch(list, SearchKey);

            if (index == -1)

            {

                Console.WriteLine("找不到資料!");

            }

            else

            {

                Console.WriteLine("查到的索引位置:" + index);

            }

            Console.ReadLine();

        }

    }

}