二分查找(折半查找)

非递归写法：

            public static int search(int left, int right, int[] array, int key)
            {

                int mid = (left + right) / 2;
                //不在当前搜索集里面
                if (key < array[0] || key > array[array.Length - 1])
                {
                    return -1;
                }
                while (left <= right)
                {

                    if (array[mid] == key)
                    {
                        return mid;
                    }
                    else if (array[mid] > key)
                    {
                        right = mid - 1;
                    }
                    else
                    {
                        left = mid + 1;
                    }
                }
                return -1;
            }

递归写法：

   public static int search(int left, int right, int[] array, int key)
            {
                int mid = (left + right) / 2;
                //不在当前搜索集里面
                if (key < array[0] || key > array[array.Length - 1])
                {
                    return -1;
                }
                while (left <= right)
                {

                    if (array[mid] == key)
                    {
                        return mid;
                    }
                    else if (array[mid] > key)
                    {
                        return search(left,mid-1,array,key);
                    }
                    else
                    {
                        return search(mid+1,right,array,key);
                    }
                }
                return -1;
            }

Main函数：

 public static void Main()
            {
                int[] array = { 10, 14, 16, 18, 25, 30, 45, 65, 76, 81, 90, 102, 156 };
                foreach(int a in array)
                {
                    Console.Write(a+" ");

                }
                Console.WriteLine();
                Console.WriteLine("查找10000："+search(1,array.Length,array,10000));
                Console.WriteLine("查找5：" + search(1,array.Length,array, 5));
                Console.WriteLine("查找18：" + search(1, array.Length , array, 18));
                Console.ReadKey();
            }