#### 递归二分法

```csharp
    /// <summary>
    /// 二分查找法
    /// </summary>
    private int DivSearch(int num, int low, int high, int [] arr)
    {
        int middle = (low + high) / 2 ;
        while (low <= high)
        {
            if (num < arr[middle])
            {
                return DivSearch(num, low, middle - 1, arr);
            }
            else if (num > arr[middle])
            {
                return DivSearch(num, middle + 1, high, arr);
            }
            else
            {
                return middle;
            }
        }
        return middle;
    }
```

