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We describe a new external memory data structure, the buffered repository tree, and use it to provide the first non-trivial external memory algorithm for directed breadth-first search (BFS) and an improved external algorithm for directed depth-first search. We also demonstrate the equivalence of various formulations of external undirected BFS, and we use… (More)

We present a new linear-time algorithm to find the immediate dominators of all vertices in a flowgraph. Our algorithm is simpler than previous linear-time algorithms: rather than employ complicated data structures, we combine the use of microtrees and memoization with new observations on a restricted class of path compressions. We have implemented our… (More)

We present a new approach for designing external graph algorithms and use it to design simple, deterministic and randomized external algorithms for computing connected components, minimum spanning forests, bottleneck minimum spanning forests, maximal independent sets (randomized only), and maximal matchings in undirected graphs. Our I/O bounds compete with… (More)

We formalize the problem of maintaining views of graphs. These are graphs induced by the contraction of vertex subsets that are defined by associated hierarchies. We provide data structures that allow applications to refine and coarsen such views interactively and efficiently, in time linear in the number of changes induced by any exploration operation. The… (More)

We introduce the tree cross-product problem, which abstracts a data structure common to applications in graph visualization, string matching, and software analysis. We design solutions with a variety of tradeoffs, yielding improvements and new results for these applications.

We study the problem of compressing massive tables. We devise a novel compression paradigm—training for lossless compression— which assumes that the data exhibit dependencies that can be learned by examining a small amount of training material. We develop an experimental methodology to test the approach. Our result is a system, pzip, which outperforms gzip… (More)

We present two new data structure tools—disjoint set union with bottom-up linking, and pointer-based radix sort—and combine them with bottom-level microtrees to devise the first linear-time pointer-machine algorithms for off-line least common ancestors, minimum spanning tree (MST) verification , randomized MST construction, and computing domina-tors in a… (More)

We design a variation of skip lists that performs well for generally biased access sequences. Given n items, each with a positive weight w i , 1 ≤ i ≤ n, the time to access item i is O 1 + log W wi , where W = n i=1 w i ; the data structure is dynamic. We present two instan-tiations of biased skip lists, one of which achieves this bound in the worst case,… (More)

Construction of both text-to-speech synthesis (TTS) and automatic speech recognition (ASR) systems involves usage of speech data bases. These data bases usually consist of read text, which means that one has significant control over the content of the data base. Here we address how one can take advantage of this control, by discussing a number of variants… (More)

Suppose we are given a set of objects that cover a region and a duration associated with each object. Viewing the objects as jobs, can we schedule their beginning times to maximize the length of time that the original region remains covered? We call this problem the SENSOR COVER PROBLEM. It arises in the context of covering a region with sensors. For… (More)