Prof. Dr. Tobias Friedrich

Anton Krohmer

Research Group Algorithm Engineering
Hasso Plattner Institute

Office: A-1.7/8
Tel.: +493315509-414
E-Mail: Anton.Krohmer(at)hpi.de


[2017] [2016] [2015] [2014] [2012] [2010]

2017 [ to top ]

  • submission ESA 2017.pdf
    Friedrich, Tobias; Krohmer, Anton; Rothenberger, Ralf; Sauerwald, Thomas; Sutton, Andrew M. Bounds on the Satisfiability Threshold for Power Law Distributed Random SAT. European Symposium on Algorithms (ESA) 2017
  • hypclique.pdf
    Bläsius, Thomas; Friedrich, Tobias; Krohmer, Anton Cliques in Hyperbolic Random Graphs. Algorithmica 2017
  • 0001KRS17.pdf
    Friedrich, Tobias; Krohmer, Anton; Rothenberger, Ralf; Sutton, Andrew M. Phase Transitions for Scale-Free SAT Formulas. Association for the Advancement of Artificial Intelligence (AAAI) 2017: 3893-3899

2016 [ to top ]

  • HyperbolicRandomGraphsSeparatorsAndTreewidth.pdf
    Bläsius, Thomas; Friedrich, Tobias; Krohmer, Anton Hyperbolic Random Graphs: Separators and Treewidth. European Symposium on Algorithms (ESA) 2016: 15:1-15:16
  • EfficientEmbeddingOfScaleFreeGraphsInTheHyperbolicPlane.pdf
    Bläsius, Thomas; Friedrich, Tobias; Krohmer, Anton; Laue, Sören Efficient Embedding of Scale-Free Graphs in the Hyperbolic Plane. European Symposium on Algorithms (ESA) 2016: 16:1-16:18
    EATCS Best Paper Award

2015 [ to top ]

  • FriedrichK15.pdf
    Friedrich, Tobias; Krohmer, Anton Cliques in hyperbolic random graphs. International Conference on Computer Communications (INFOCOM) 2015: 1544-1552
  • OnTheDiameterOfHyperbolicRandomGraphs.pdf
    Friedrich, Tobias; Krohmer, Anton On the Diameter of Hyperbolic Random Graphs. International Colloquium on Automata, Languages and Programming (ICALP) 2015: 614-625
  • UnboundedDiscrepancyOfDeterministicRandomWalksOnGrids.pdf
    Friedrich, Tobias; Katzmann, Maximilian; Krohmer, Anton Unbounded Discrepancy of Deterministic Random Walks on Grids. International Symposium on Algorithms and Computation (ISAAC) 2015: 212-222
  • ParameterizedCliqueOnInhomogeneousRandomGraphsJournal.pdf
    Friedrich, Tobias; Krohmer, Anton Parameterized clique on inhomogeneous random graphs. Discrete Applied Mathematics 2015: 130-138

2014 [ to top ]

  • De-AnonymizationOfHeterogeneousRandomGraphsInQuasilinearTime.pdf
    Bringmann, Karl; Friedrich, Tobias; Krohmer, Anton De-anonymization of Heterogeneous Random Graphs in Quasilinear Time. European Symposium on Algorithms (ESA) 2014: 197-208

2012 [ to top ]

  • BaumbachFKKMP12.pdf
    Baumbach, Jan; Friedrich, Tobias; Kötzing, Timo; Krohmer, Anton; Müller, Joachim; Pauling, Josch Efficient Algorithms for Extracting Biological Key Pathways with Global Constraints. Genetic and Evolutionary Computation Conference (GECCO) 2012: 169-176
  • EfficientKeyPathwayMiningCombiningNetworksAndOMICSDataJournal.pdf
    Alcaraz, Nicolas; Friedrich, Tobias; Kötzing, Timo; Krohmer, Anton; Müller, Joachim; Pauling, Josch; Baumbach, Jan Efficient Key Pathway Mining: Combining Networks and OMICS Data. Integrative Biology 2012: 756-764
  • ParameterizedCliqueOnScale-FreeNetworks.pdf
    Friedrich, Tobias; Krohmer, Anton Parameterized Clique on Scale-Free Networks. International Symposium on Algorithms and Computation (ISAAC) 2012: 659-668

2010 [ to top ]

  • ratfish2010.pdf
    Backes, Michael; Ciobotaru, Oana; Krohmer, Anton RatFish: A File Sharing Protocol Provably Secure against Rational Users. European Symposium on Research in Computer Security (ESORICS) 2010: 607-625

Other Works

  • Finding Cliques in Scale-Free Networks. [pdf]
    Master Thesis, 2012.
  • Rational File Sharing. [pdf]
    Bachelor Thesis, 2009.

Nice Riddles

Here's a collection of my favorite riddles.

Battling Coins

You and your friend are playing the following game on a rectangular table. Each of you has an unlimited supply of equally-sized coins. Whenever it's a player's turn, the player has to put down a coin on an unoccupied space on the table. In particular, the coin cannot overlap with previously placed coins.

The first player who cannot put down a coin loses.

Do you want to go first or second in this game? What is a winning strategy?

Squaring Squares

Assume you are given four points in the plane that form a square with side length 1. You are allowed to modify the position of the points as follows: You can mirror a point at another one of the four points.

Is it possible to create a square with side length 2 using only these operations?

Robot Meeting

Two robots land safely with their parachutes on the integer line. They leave their parachute at the landing position and then proceed to execute their coded programs. They both contain exactly the same program. Your task is to write this program in such a way that they will eventually meet. You have access to the following operations:

  • Move left
  • Move right
  • GOTO x (where x is a line number in your code)
  • If there is a parachute at your position, skip the next line of code

Your program should not be longer than 10 lines.

Spiders, Spiders Everywhere!

This riddle is a little different, and it is hard to get all constraints straight, but let's try:

You inherited a room in which you intend to sleep. Unfortunately, the room is haunted, and spiders can spawn on the walls and on the ceiling. A spider can crawl essentially everywhere, and it can also let itself drop from wherever it is hanging right now.

Your task is to place your bed inside the room such that you can sleep without being pestered by spiders. To this end, you can build immovable structures (in particular, you cannot build a house inside your room since you cannot enter the room without a door); and you can use water.

Spiders hate water. While you can step over it (if it is narrow enough), they cannot cross water. However, you cannot just "place water" in your room; the laws of gravity still apply. To this end, if you want to place water somewhere, you will have to build a structure such that it contains the water. The structures are of non-negligible thickness, i.e., you cannot contain water within walls of "thickness almost 0." If in doubt, there is always a spider small enough that can land on the wall.

For instance, it is possible to build a small moat around your bed. Then, spiders cannot enter your bed via the floor. They still can, however, enter your bed by crawling on the ceiling and then dropping in your mouth while you sleep.

How can you prevent spiders from reaching your bed?