"E?ziente Algorithmen" was the title of the ?rst book by Kurt Mehlhorn in 1977. It was meant as a text for graduate students and published in German by Teubner-Verlag. We decided to adopt this title 32 years later for this Festschrift in honor of Kurt on the occasion of his 60th birthday. It contains contributions by his former PhD students, many of whom are now university teachers themselves, and colleagues with whom he cooperated closely within his career. It is our pleasure that even Kurt's former PhD advisor, Bob Constable from Cornell University,kindlyagreedtocontribute.Manyofthecontributionswerepresented at a colloquium held in Kurt's honor on August 27 and 28, 2009 in Saarbrucken, Germany. This Festschriftshowsclearlyhowthe ?eld ofalgorithmicshas developedand matured in the decades since Kurt wrote his book with the same title. The classic approach based on discrete mathematics and computability and complexity theory continues to be the foundation of the ?eld with ever new and important challenges as the ?rst chapters of this Festschrift show. Kurt has contributed signi?cantly to classical algorithmics and gained worldwide repu- tion. Starting from research in computability theory in his PhD thesis he made major contributions to complexity theory, graph algorithms, data structures, and was one of the ?rst to recognize the signi?cance of computational geometry contributing one of the early textbooks on the subject.

ICALP 2009, the 36th edition of the International Colloquium on Automata, Languages and Programming, was held on the island of Rhodes, July 6-10, 2009. ICALP is a series of annual conferences of the European Association for Theoretical Computer Science (EATCS) which ?rst took place in 1972. This year, the ICALP program consisted of the established track A (focusing on algorithms, complexity and games) and track B (focusing on logic, automata, semantics and theory of programming), and of the recently introduced track C (in 2009 focusing on foundations of networked computation). In response to the call for papers, the Program Committee received 370 s- missions: 223 for track A, 84 for track B and 63 for track C. Out of these, 108 papers were selected for inclusion in the scienti?c program: 62 papers for track A, 24 for track B and 22 for track C. The selection was made by the Program Committees based on originality, quality, and relevance to theoretical computer science. The quality of the manuscripts was very high indeed, and many dese- ing papers could not be selected. ICALP 2009 consisted of ?ve invited lectures and the contributed papers.

ICALP 2009, the 36th edition of the International Colloquium on Automata, Languages and Programming, was held on the island of Rhodes, July 6-10, 2009. ICALP is a series of annual conferences of the European Association for Theoretical Computer Science (EATCS) which ?rst took place in 1972. This year, the ICALP program consisted of the established track A (focusing on algorithms, complexity and games) and track B (focusing on logic, automata, semantics and theory of programming), and of the recently introduced track C (in 2009 focusing on foundations of networked computation). In response to the call for papers, the Program Committee received 370 s- missions: 223 for track A, 84 for track B and 63 for track C. Out of these, 108 papers were selected for inclusion in the scienti?c program: 62 papers for track A, 24 for track B and 22 for track C. The selection was made by the Program Committees based on originality, quality, and relevance to theoretical computer science. The quality of the manuscripts was very high indeed, and many dese- ing papers could not be selected. ICALP 2009 consisted of ?ve invited lectures and the contributed papers. Thisvolumeoftheproceedingscontainsallcontributedpaperspresentedintrack AtogetherwiththepapersbytheinvitedspeakersKurtMehlhorn(Max-Planck- Institut fu ..r Informatik, Saarbru ..cken)and Christos Papadimitriou(University of California at Berkeley). A companion volume contains all contributed papers presented at the conference in track B and track C, together with the papers by the invited speakers Georg Gottlob (University of Oxford), Tom Henzinger ' (EcolePolytechniqueF' ed' eraledeLausanne),andNoamNisan(Google,TelAviv, and Hebrew University).

This volume contains the 70 contributed papers and abstracts of two invited l- tures presented at the 12th Annual European Symposium on Algorithms (ESA 2004), held in Bergen, Norway, September 14-17, 2004. The papers in each s- tion of the proceedings are arranged alphabetically. The three distinguished - vited speakers were David Eppstein, Michael Fellows and Monika Henzinger. As in the last two years, ESA had two tracks, with separate program c- mittees, which dealt respectively with: - the design and mathematical analysis of algorithms (the "Design and A- lysis" track); - real-world applications, engineering and experimental analysis of algorithms (the "Engineering and Applications" track). Previous ESAs were held at Bad Honnef, Germany (1993); Utrecht, The Netherlands (1994); Corfu, Greece (1995); Barcelona, Spain (1996); Graz, A- tria (1997); Venice, Italy (1998); Prague, Czech Republic (1999); Saarbruc .. ken, ? Germany (2000); Arhus, Denmark (2001); Rome, Italy (2002); and Budapest, Hungary (2003). The predecessor to the Engineering and Applications track of ESA was the annual Workshop on Algorithm Engineering (WAE). Previous WAEs were held in Venice, Italy (1997); Saarbruc .. ken, Germany (1998); London, ? UK (1999); Saarbruc .. ken, Germany (2000); and Arhus, Denmark (2001). The proceedings of the previous ESAs were published as Springer-Verlag's LNCS volumes 726, 855, 979, 1284, 1461, 1643, 1879, 2161, 2461, and 2832. The proceedingsoftheWAEsfrom1999onwardswerepublishedasSpringer-Verlag's LNCS volumes 1668, 1982, and 2141.