Abstract
The well known binary search method can be described as the process of identifying some marked node from a line graph T by successively querying edges. An edge query e asks in which of the two subpaths induced by T ∖ e the marked node lies. This procedure can be naturally generalized to the case where T = (V,E) is a tree instead of a line. The problem of determining a tree search strategy minimizing the number of queries in the worst case is solvable in linear time [Onak et al. FOCS’06, Mozes et al. SODA’08].
Here we study the average-case problem, where the objective function is the weighted average number of queries to find a node An involved analysis shows that the problem is \({\cal NP}\)-complete even for the class of trees with bounded diameter, or bounded degree.
We also show that any optimal strategy (i.e., one that minimizes the expected number of queries) performs at most O( Δ(T) ( log|V| + logw(T))) queries in the worst case, where w(T) is the sum of the node weights and Δ(T) is the maximum degree of T. This structural property is then combined with a non-trivial exponential time algorithm to provide an FPTAS for the bounded degree case.
Most omitted proofs can be found at http://arxiv.org/abs/0904.3503.
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References
Adler, M., Heeringa, B.: Approximating optimal binary decision trees. In: Goel, A., Jansen, K., Rolim, J.D.P., Rubinfeld, R. (eds.) APPROX and RANDOM 2008. LNCS, vol. 5171, pp. 1–9. Springer, Heidelberg (2008)
Arkin, E., Meijer, H., Mitchell, J., Rappaport, D., Skiena, S.: Decision trees for geometric models. Int. Jour. of Comp. Geom. and Appl. 8(3), 343–364 (1998)
Ben-Asher, Y., Farchi, E., Newman, I.: Optimal search in trees. SIAM Journal on Computing 28(6), 2090–2102 (1999)
Carmo, R., Donadelli, J., Kohayakawa, Y., Laber, E.: Searching in random partially ordered sets. Theoretical Computer Science 321(1), 41–57 (2004)
Chakaravarthy, V., Pandit, V., Roy, S., Awasthi, P., Mohania, M.: Decision trees for entity identification: Approximation algorithms and hardness results. In: PODS, pp. 53–62 (2007)
Daskalakis, C., Karp, R., Mossel, E., Riesenfeld, S., Verbin, E.: Sorting and selection in posets. In: SODA, pp. 392–401 (2009)
de la Torre, P., Greenlaw, R., Schäffer, A.: Optimal edge ranking of trees in polynomial time. Algorithmica 13(6), 592–618 (1995)
Dereniowski, D.: Edge ranking and searching in partial orders. DAM 156, 2493–2500 (2008)
Faigle, U., Lovász, L., Schrader, R., Turán, G.: Searching in trees, series-parallel and interval orders. SICOMP: SIAM Journal on Computing 15 (1986)
Garey, M.: Optimal binary identification procedures. SIAP 23(2), 173–186 (1972)
Garey, M., Johnson, D.: Computers and Intractability: A Guide to the Theory of NP–Completeness. Freeman, New York (1979)
Garsia, A., Wachs, M.: A new algorithm for minimum cost binary trees. SIAM Journal on Computing 6(4), 622–642 (1977)
Hu, T., Tucker, A.: Optimal computer search trees and variable-length alphabetic codes. SIAM Journal on Applied Mathematics 21(4) (1971)
Hyafil, L., Rivest, R.: Constructing optimal binary decision trees is NP-complete. Information Processing Letters 5(1), 15–17 (1976)
Ibarra, O., Kim, C.: Fast approximation algorithms for the knapsack and sum of subset problems. Journal of the ACM 22(4), 463–468 (1975)
Knuth, D.: The Art of Computer Programming, Sorting and Searching, vol. 3. Addison-Wesley, Reading (1973)
Kosaraju, R., Przytycka, T., Borgstrom, R.: On an optimal split tree problem. In: Dehne, F., Gupta, A., Sack, J.-R., Tamassia, R. (eds.) WADS 1999. LNCS, vol. 1663, pp. 157–168. Springer, Heidelberg (1999)
Laber, E., Molinaro, M.: An approximation algorithm for binary searching in trees. In: Aceto, L., Damgård, I., Goldberg, L.A., Halldórsson, M.M., Ingólfsdóttir, A., Walukiewicz, I. (eds.) ICALP 2008, Part I. LNCS, vol. 5125, pp. 459–471. Springer, Heidelberg (2008)
Laber, E., Nogueira, L.: On the hardness of the minimum height decision tree problem. Discrete Applied Mathematics 144(1-2), 209–212 (2004)
Lam, T., Yue, F.: Optimal edge ranking of trees in linear time. In: SODA, pp. 436–445 (1998)
Larmore, H., Hirschberg, D.S., Larmore, L.L., Molodowitch, M.: Subtree weight ratios for optimal binary search trees. Technical report (1986)
Linial, N., Saks, M.: Searching ordered structures. J. of Algorithms 6 (1985)
Lipman, M., Abrahams, J.: Minimum average cost testing for partially ordered components. IEEE Transactions on Information Theory 41(1), 287–291 (1995)
Mozes, S., Onak, K., Weimann, O.: Finding an optimal tree searching strategy in linear time. In: SODA, pp. 1096–1105 (2008)
Onak, K., Parys, P.: Generalization of binary search: Searching in trees and forest-like partial orders. In: FOCS, pp. 379–388 (2006)
Schäffer, A.: Optimal node ranking of trees in linear time. IPL 33, 91–96 (1989)
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Jacobs, T., Cicalese, F., Laber, E., Molinaro, M. (2010). On the Complexity of Searching in Trees: Average-Case Minimization. In: Abramsky, S., Gavoille, C., Kirchner, C., Meyer auf der Heide, F., Spirakis, P.G. (eds) Automata, Languages and Programming. ICALP 2010. Lecture Notes in Computer Science, vol 6198. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-14165-2_45
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