https://blog.faceutil.com/2017/03/14/%ec%a4%91%eb%b3%b5-%ed%8c%8c%ec%9d%bc-%ea%b2%80%ec%83%89-%ed%94%84%eb%a1%9c%ea%b7%b8%eb%9e%a8-fast-duplicate-file-finder-%e3%83%9b/