This proceedings volume contains the accepted papers and invited talks p- sented at the 4th International Workshop of E?cient and Experimental Al- rithms (WEA 2005), that was held May 10-13, on Santorini Island, Greece. The WEA events are intended to be an international forum for research on the design, analysis and especially the experimental implementation, evaluation and engineering of algorithms, as well as on combinatorial optimization and its applications. The?rstthreeworkshopsinthisserieswereheldinRiga(2001),MonteVerita (2003) and Rio de Janeiro (2004). Thisvolumecontains3invitedpapersrelatedtocorrespondingkeynotetalks: by Prof. Christos Papadimitriou (University of California at Berkeley, USA), Prof. David Bader (University of New Mexico, USA) and Prof. Celso Ribeiro (University of Rio de Janeiro, Brazil). This proceedings includes 54 papers (47 regular and 7 short), selected out of a record number of 176 submissions. Each paper was reviewed by at least 2 Program Committee members, while many papers got 3 or 4 reviews. A total number of 419 reviews were solicited, with the help of trusted external referees. In addition to the 54 papers included in this volume, 6papers were accepted as poster presentations: these papers were published in a separate poster p- ceedings volume by CTI Press and a major publisher in Greece, "Ellinika Gr- mata." The presentation of these posters at the event was expected to create a fruitful discussion on interesting ideas.

Table of Contents:
Invited Talks.- T? ??? ?í ? ??í?? ? The Interaction Between Algorithms and Game Theory.- Using an Adaptive Memory Strategy to Improve a Multistart Heuristic for Sequencing by Hybridization.- High-Performance Algorithm Engineering for Large-Scale Graph Problems and Computational Biology.- Contributed Regular Papers.- The “Real” Approximation Factor of the MST Heuristic for the Minimum Energy Broadcasting.- Implementing Minimum Cycle Basis Algorithms.- Rounding to an Integral Program.- Rectangle Covers Revisited Computationally.- Don’t Compare Averages.- Experimental Results for Stackelberg Scheduling Strategies.- An Improved Branch-and-Bound Algorithm for the Test Cover Problem.- Degree-Based Treewidth Lower Bounds.- Inferring AS Relationships: Dead End or Lively Beginning?.- Acceleration of Shortest Path and Constrained Shortest Path Computation.- A General Buffer Scheme for the Windows Scheduling Problem.- Implementation of Approximation Algorithms for the Multicast Congestion Problem.- Frequency Assignment and Multicoloring Powers of Square and Triangular Meshes.- From Static Code Distribution to More Shrinkage for the Multiterminal Cut.- Partitioning Graphs to Speed Up Dijkstra’s Algorithm.- Efficient Convergence to Pure Nash Equilibria in Weighted Network Congestion Games.- New Upper Bound Heuristics for Treewidth.- Accelerating Vickrey Payment Computation in Combinatorial Auctions for an Airline Alliance.- Algorithm Engineering for Optimal Graph Bipartization.- Empirical Analysis of the Connectivity Threshold of Mobile Agents on the Grid.- Multiple-Winners Randomized Tournaments with Consensus for Optimization Problems in Generic Metric Spaces.- On Symbolic Scheduling Independent Tasks with Restricted Execution Times.- A Simple Randomizedk-Local Election Algorithm for Local Computations.- Generating and Radiocoloring Families of Perfect Graphs.- Efficient Implementation of Rank and Select Functions for Succinct Representation.- Comparative Experiments with GRASP and Constraint Programming for the Oil Well Drilling Problem.- A Framework for Probabilistic Numerical Evaluation of Sensor Networks: A Case Study of a Localization Protocol.- A Cut-Based Heuristic to Produce Almost Feasible Periodic Railway Timetables.- GRASP with Path-Relinking for the Weighted Maximum Satisfiability Problem.- New Bit-Parallel Indel-Distance Algorithm.- Dynamic Application Placement Under Service and Memory Constraints.- Integrating Coordinated Checkpointing and Recovery Mechanisms into DSM Synchronization Barriers.- Synchronization Fault Cryptanalysis for Breaking A5/1.- An Efficient Algorithm for ?-Approximate Matching with ?-Bounded Gaps in Musical Sequences.- The Necessity of Timekeeping in Adversarial Queueing.- BDDs in a Branch and Cut Framework.- Parallel Smith-Waterman Algorithm for Local DNA Comparison in a Cluster of Workstations.- Fast Algorithms for Weighted Bipartite Matching.- A Practical Minimal Perfect Hashing Method.- Efficient and Experimental Meta-heuristics for MAX-SAT Problems.- Experimental Evaluation of the Greedy and Random Algorithms for Finding Independent Sets in Random Graphs.- Local Clustering of Large Graphs by Approximate Fiedler Vectors.- Almost FPRAS for Lattice Models of Protein Folding.- Vertex Cover Approximations: Experiments and Observations.- GRASP with Path-Relinking for the Maximum Diversity Problem.- How to Splay for loglogN-Competitiveness.- Distilling Router Data Analysis for Faster and Simpler Dynamic IP Lookup Algorithms.- Contributed Short Papers.- Optimal Competitive OnlineRay Search with an Error-Prone Robot.- An Empirical Study for Inversions-Sensitive Sorting Algorithms.- Approximation Algorithm for Chromatic Index and Edge-Coloring of Multigraphs.- Finding, Counting and Listing All Triangles in Large Graphs, an Experimental Study.- Selecting the Roots of a Small System of Polynomial Equations by Tolerance Based Matching.- Developing Novel Statistical Bandwidths for Communication Networks with Incomplete Information.- Dynamic Quality of Service Support in Virtual Private Networks.