1. School of Computer Science, Qufu Normal University, Rizhao 276826, China
2. Key Laboratory for Intelligent Control Technique of Shandong Province, Qufu Normal University, Rizhao 276826, China
3. Department of Computer Science, The University of Hong Kong, Pokfulam, Hong Kong
4. School of Mathematics, Shandong University, Shandong, Jinan 250100, China