二进制搜索-如果上限大于或等于键，则答案错误

Question

问题是元素的上限。当等于key时，算法返回-1；当大于key时，返回最高索引。

我的任务是在数组中不存在元素时返回-1。

算法：

public static int BinarySearch(int[] arr, int low, int high, int key)
        {
            if(high<low)
            {
                return low - 1;
            }

            int mid = low + ((high - low) / 2);
            //this 'if' is my solution when key is more than high bound element
            if (mid == high)
            {
                if (arr[mid] != key)
                {
                    return -1;
                }
            }
            if (arr[mid] == key)
            {
                return mid;
            }
            else if (arr[mid] < key)
            {
                return BinarySearch(arr, mid + 1, high, key);
            }
            else
            {
                return BinarySearch(arr, low, mid - 1, key);
            }
        }

驱动程序代码：

static void Main(string[] args)
        {
            string[] arr = Console.ReadLine().Split(' ');
            int[] n = new int[Convert.ToInt32(arr[0])];
            for(int i =1;i<Convert.ToInt32(arr[0]);i++)
            {
                n[i-1] = Convert.ToInt32(arr[i]);
            }
            string[] arr2 = Console.ReadLine().Split(' ');
            int[] k = new int[Convert.ToInt32(arr2[0])];
            for(int i = 1; i< Convert.ToInt32(arr2[0]);i++)
            {
                k[i-1] = Convert.ToInt32(arr2[i]);
            }
            int[] answer = new int[Convert.ToInt32(arr2[0])];
            for(int i = 0;i< Convert.ToInt32(arr[0]);i++)
            {
                    answer[i] = BinarySearch(n, 0, n.Length - 1 , k[i]);
            }

            for (int i = 0; i < Convert.ToInt32(arr[0]); i++)
            {
                Console.Write(answer[i]+" ");
            }

        }

输入：

first line: 5 1 2 3 4 5
second line: 5 1 2 3 4 5
it should return : 0 1 2 3 4 
mine returned: 0 1 2 3 -1

任何帮助将不胜感激。