This algorithm aims to compare the files within two folders. The files within B folder are more than the A folder. Put these files which are not in A folder into a separate folder C. If files already in C folder, pass it.

How

Use the nature and operation of the collection.

Implemented in Python

import os
import shutil


def incremental_update(a_folder_path: str,
                       b_folder_path: str,
                       c_folder_path: str) -> None:
    """Incremental update.

    Args:
        a_folder_path str: A folder path.
        b_folder_path str: B folder path.
        c_folder_path str: C folder path.

    Return:
        None
    """
    # Compare files between 3 folders.
    c_files = (set(os.listdir(a_folder_path))
               - set(os.listdir(b_folder_path))
               - set(os.listdir(c_folder_path)))

    if not os.path.isdir(c_folder_path):
        os.mkdir(c_folder_path)

    def _copy(f_path: str) -> None:
        """Copy file from B to C.

        Args:
            f_path: str. The file in B folder.
        """
        shutil.copy(
            os.path.join(b_folder_path, f_path),
            os.path.join(c_folder_path, f_path))

    for f_path in c_files:
        _copy(f_path)