递归折半查找算法
def recursive_binary_search(arr, low, high, key):
if low <= high:
mid = (low + high) // 2
if arr[mid] == key:
return mid
elif key < arr[mid]:
return recursive_binary_search(arr, low, mid-1, key)
else:
return recursive_binary_search(arr, mid+1, high, key)
return -1