def find_max(nums):
    if not nums:
        raise ValueError("输入数组不能为空")
    if len(nums) == 1:
        return nums[0]
    mid = len(nums) // 2
    return max(
        find_max(nums[:mid]),
        find_max(nums[mid:])
    )
print(find_max([1,2,2,11,21,1,2,3]))