| Linear-Time Pointer-Machine Algorithms for Path-Evaluation Problems on Trees and Graphs (2002) | |||||||||
Abstract | |||||||||
| We present algorithms that run in linear time on pointer machines for a collection of problems, each of which either directly or indirectly requires the evaluation of a function defined on paths in a tree. These problems previously had linear-time algorithms but only for random-access machines (RAMs); the best pointer-machine algorithms were super-linear by an inverse-Ackermann-function factor. Our algorithms are also simpler, in some cases substantially, than the previous linear-time RAM algorithms. Our improvements come primarily from three new ideas: a refined analysis of path compression that gives a linear bound if the compressions favor certain nodes, a pointer-based radix sort as a replacement for table-based methods, and a more careful partitioning of a tree into easily managed parts. Our algorithms compute nearest common ancestors off-line, verify and construct minimum spanning trees, do interval analysis on a flowgraph, find the dominators of a flowgraph, and build the component tree of a weighted tree.. Comment: 41 pages; 10 figures; 1 table; 65 references. This work is partially covered by the extended abstracts, ``Linear-Time Pointer-Machine Algorithms for Least Common Ancestors, MST Verification, and Dominators,'' Proc. 30th ACM Symp. on Theory of Computing, pp. 279-888, 1998, and ``Finding Dominators Revisited,'' Proc. 15th ACM-SIAM Symp. on Discrete Algorithms, pp. 862-871, 2004 | |||||||||
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