Example 1:
Input: nums = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4
Example 2:

Input: nums = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1

下面為 Example 1 解法

       static void Main(string[] args)
       {
           BinarySearch();
       }

       private static void BinarySearch()
       {
           var nums = new int[] { -1, 0, 3, 5, 9, 12 };
           int target = 9;
           var result = BinarySearch(nums, target);
           Console.WriteLine($"目標索引:{result}");
           Console.ReadKey();
       }

       /// <summary>
       /// 二分收詢
       /// </summary>
       /// <param name="nums">數組</param>
       /// <param name="target">目標值</param>
       /// <exception cref="NotImplementedException"></exception>
       private static int BinarySearch(int[] nums, int target)
       {
           int left = 0;
           int right = nums.Length - 1;

           while (left <= right)
           {
               int mid = (right + left) / 2;

               if (nums[mid] == target)
               {
                   return mid;
               }
               else if (nums[mid] < target)
               {
                   left = mid + 1;
               }
               else
               {
                   right = mid - 1;
               }
           }

           return -1;
       }