Scapegoat trees: a comparative performance assessment

Η εργασία αυτή παρουσιάζει και αναλύει μια εναλλακτική μέθοδο για την αποδοτική εξισορρόπηση δυαδικών δέντρων αναζήτησης. Τα δέντρα scapegoat είναι ελαφρώς ισορροπημένα και ανακατασκευάζουν μέρη τους υπό ορισμένες συνθήκες. Η amortized χρονική πολυπλοκότητα για κάθε λειτουργία INSERT ή REMOVE είναι Ο(logn), ενώ η worst-case πραγματική χρονική πολυπλοκότητα μιας FIND είναι Ο(logn). Τα δέντρα scapegoat, σε αντίθεση με τις περισσότερες υλοποιήσεις αυτεξισορροπούμενων BST, δεν απαιτούν επιπλέον δεδομένα (π.χ. χρώματα, βάρη, ύψη) στους κόμβους των δέντρων. Χρησιμοποιούνται διάφορες μετρικές και δοκιμές για τη σύγκριση των δέντρων AVL και scapegoat ως προς τη λειτουργικότητά τους. Τέλος, παρέχουμε δεδομένα ως προς την επίδοση των δέντρων scapegoat σε πιθανές εφαρμογές πραγματικού χρόνου.This Thesis presents and analyzes an alternative tree scheme for the efficient balancing of binary search trees. Scapegoat trees are loosely balanced and restructure parts of themselves on certain conditions. The amortized time complexity for each INSERT or REMOVE operation is Ο(logn), while the worst-case real-time complexity of a FIND one is Ο(logn). Scapegoat trees, unlike most self-balancing BST implementations, do not require extra data (e.g. colors, weights, heights) in the tree nodes. Various metrics and tests are used to compare AVL and scapegoat trees on their functionality. Finally, we provide data as to the performance of scapegoat trees in potential real-time applications

Top-Down Skiplists

We describe todolists (top-down skiplists), a variant of skiplists (Pugh 1990) that can execute searches using at most $\log_{2-\varepsilon} n + O(1)$ binary comparisons per search and that have amortized update time $O(\varepsilon^{-1}\log n)$. A variant of todolists, called working-todolists, can execute a search for any element $x$ using $\log_{2-\varepsilon} w(x) + o(\log w(x))$ binary comparisons and have amortized search time $O(\varepsilon^{-1}\log w(w))$. Here, $w(x)$ is the "working-set number" of $x$. No previous data structure is known to achieve a bound better than $4\log_2 w(x)$ comparisons. We show through experiments that, if implemented carefully, todolists are comparable to other common dictionary implementations in terms of insertion times and outperform them in terms of search times.Comment: 18 pages, 5 figure

"It´s hard for me to cope with life. With the dead it´s easier" : Dina Wardi´s book about the children of the Holocaust

Rezension des Werkes: Dina Wardi, Memorial Candles: Children of the Holocaust. London, Taylor & Francis Books Ltd, 1992. 288 pp. (Deutsche Ausgabe: Siegel der Erinnerung. Das Trauma des Holocaust – Psychotherapie mit den Kindern der Überlebenden

The Lamb of God and the Forgiveness of Sin(s) in the Fourth Gospel

The article presents a speech by Sandra M. Schneiders of the Jesuit School of Theology of Santa Clara University, delivered at the 73rd International Meeting of the Catholic Biblical Association of America, which was held at the Loyola Marymount University in Los Angeles, California, July 31-August 3, 2010, in which she discussed the violence issue and the role of Christian Scripture in alleviating such dilemma, the Messiahship of Jesus Christ, and God\u27s salvific plan to mankind