Authors: Bojan Djordjevic Joachim Gudmundsson Anh Pham Thomas Wolle
Publish Date: 2009/11/21
Volume: 60, Issue: 4, Pages: 829-852
Abstract
We are given a trajectory mathcalT and an area mathcalA mathcalT might intersect mathcalA several times and our aim is to detect whether mathcalT visits mathcalA with some regularity eg what is the longest time span that a GPSGSM equipped elephant visited a specific lake on a daily weekly or yearly basis where the elephant has to visit the lake most of the days weeks or years but not necessarily on every day week or yearDuring the modelling of such applications we encountered an elementary problem on bitstrings that we call LDS LongestDenseSubstring The bits of the bitstring correspond to a sequence of regular time points in which a bit is set to 1 if and only if the trajectory mathcal T intersects the area mathcalA at the corresponding time point For the LDS problem we are given a string s as input and want to output a longest substring of s such that the ratio of 1’s in the substring is at least a certain thresholdIn our model LDS is a core problem for many applications that aim at detecting regularity of mathcalT intersecting mathcalA We propose an optimal algorithm to solve LDS and also for related problems that are closer to applications we provide efficient algorithms for detecting regularity
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