1. College of Computer Science, Chongqing University, Chongqing 400044, China
2. School of Computer Science and Engineering, Chongqing Three Gorges University, Chongqing 404100, China
3. Key Laboratory of Intelligent Information Processing and Control, Chongqing Three Gorges University, Chongqing 404100, China
4. College of Mathematics and Statistics, Chongqing Three Gorges University, Chongqing 404100, China
5. Department of Mathematics, University of Ibadan, Ibadan 200005, Nigeria