给定如下Python代码：

def find_max(nums):
    if not nums:
        raise ValueError("输入数组不能为空")
    def _find_max(left, right):
        if left == right:
            return nums[left]
        mid = (left + right) // 2
        return max(
            _find_max(left, mid),
            _find_max(mid + 1, right)
        )
    return _find_max(0, len(nums) - 1)

print(find_max([3,39,1,31,1,2,3,12,2]))