Bidirectional maximum matching algorithm (BMM) combined positive maximal matching and reverse maximal matching algorithm, it was a more commonly used word segmentation method now, but it was low efficient and couldn’t solve the ambiguity. Therefore, an improved method was proposed combining with improved dictionary structure, and changing maximal matching word length dynamically to improve the efficiency of word segmentation. In order to get the correct segmentation results, we also proposed several rules. Compared with traditional segmentation methods, it proves that bidirectional maximal matching word segmentation with rules has higher speed and precision.

Low similarity and unreasonable design now appeared in distracters generation of English words in the process of learning English words. This paper proposed a new algorithm to solve this problem by researching Edit Distance and LCS algorithm. Comparing with traditional algorithms, the accuracy of similarity has been improved in this algorithm. Finally, combined with words’ part of speech, we generated more reasonable distracters in the experiments.

In application-layer DoS/DDoS attacks, malicious users attack the victim server by sending lots of legitimate requesting packages, which overwhelm the server bottleneck resources. Normal user’s request thus may not be satisfied. The traditional intrusion detection systems for network-layer cannot effectively identify this attack, and recent researches on this kind of attack are mainly for Web servers. This paper proposed a new defense algorithm based on user activity for topic-based Pub/Sub communication servers in mobile push notification systems. Users consuming system bottleneck resources the most can get high scores and thus are considered overactive. With some resource retaken strategy, overactive users’ connections will be dropped according to system performance level. Therefore, the system can get rid of latent threatens. Experiments indicated that this algorithm can identify normal and abnormal users well.