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A directed multigraph is said to be <i>d</i>-regular if the indegree and outdegree of every vertex is exactly <i>d</i>. By Hall's theorem, one can represent such a multigraph as a combination of at most <i>n</i><sup>2</sup> cycle covers, each taken with an appropriate multiplicity. We prove that if the <i>d</i>-regular multigraph does not contain more than(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 study the parameterizedcomplexityof three NP-hard graph completionproblems. The MINIMUM FILL-IN problem is to decide if a graph can be triangulated by adding at most k edges. We develop O(c k m) and O(k 2 mn + f(k)) algorithms for this problem on a graph with n vertices and m edges. Here f(k) is exponential in k and the constants hidden by the big-O(More)
We present algorithms to label the nodes of an XML tree which is subject to insertions and deletions of nodes. The labeling is done such that (1) we label each node immediately when it is inserted and this label remains unchanged, and (2) from a pair of labels alone, we can decide whether one node is an ancestor of the other. This problem arises in the(More)
We present approximation schemes for \dense" instances of many well-known NP-hard problems, including 0-1 quadratic-assignment, (an optimization formulation of) graph-isomorphism, min-cut-linear-arrangement, max-acyclic-subgraph, betweenness, and min-linear-arrangment. (A \dense" graph is one in which the number of edges is (n 2); denseness for the other(More)
The basic question that Economics deals with is how to " best " allocate scarce resources. The basic answer is that trade can improve everyone's welfare, and will lead to a market equilibrium: a vector of resource prices that " clear the market " and lead to an efficient allocation. Indeed, Arrow and Debreu and much further work show that such market(More)
Maximum flow and minimum s-t cut algorithms are used to solve several fundamental problems in computer vision. These problems have special structure, and standard techniques perform worse than the special-purpose Boykov-Kolmogorov (BK) algorithm. We introduce the incremental breadth-first search (IBFS) method, which uses ideas from BK but augments on(More)