50 research outputs found
AVL-trees for localized search
No full textWe present a data structure based on AVL-trees which allows an insertion or a deletion to be performed in time O(log d), where d is the distance of the position searched for from a finger which points to the end of the file. Moving a finger to a distance d costs O(log d). This result demonstrates the power of the oldest basic data structure, the AVL-tree. A special case of interest is an efficient implementation of searchable priority queues such that Deletemin requires only constant time
Finding a negative cycle in a directed graph
No full textWe present an algorithm implemented on a pointer machine which can find a negative Cycle in a directed graph in worst case Time O(n.e), where n is the number of nodes and e the number of edges, using only linear Space O(n+e). The best previous result was due to D.Maier [5]. His algorithm is running on a random access machine in worst case Time O(n(e+nlog n/log nlog n)) and uses Space O(e+nlog n/log nlog n)
Storage Efficient Trajectory Clustering and k-NN for Robust Privacy Preserving Spatio-Temporal Databases
No full textThe need to store massive volumes of spatio-temporal data has become a difficult task as GPS capabilities and wireless communication technologies have become prevalent to modern mobile devices. As a result, massive trajectory data are produced, incurring expensive costs for storage, transmission, as well as query processing. A number of algorithms for compressing trajectory data have been proposed in order to overcome these difficulties. These algorithms try to reduce the size of trajectory data, while preserving the quality of the information. In the context of this research work, we focus on both the privacy preservation and storage problem of spatio-temporal databases. To alleviate this issue, we propose an efficient framework for trajectories representation, entitled DUST (DUal-based Spatio-temporal Trajectory), by which a raw trajectory is split into a number of linear sub-trajectories which are subjected to dual transformation that formulates the representatives of each linear component of initial trajectory; thus, the compressed trajectory achieves compression ratio equal to M : 1 . To our knowledge, we are the first to study and address k-NN queries on nonlinear moving object trajectories that are represented in dual dimensional space. Additionally, the proposed approach is expected to reinforce the privacy protection of such data. Specifically, even in case that an intruder has access to the dual points of trajectory data and try to reproduce the native points that fit a specific component of the initial trajectory, the identity of the mobile object will remain secure with high probability. In this way, the privacy of the k-anonymity method is reinforced. Through experiments on real spatial datasets, we evaluate the robustness of the new approach and compare it with the one studied in our previous work
