**Chair for**** Algorithm Engineering**

Hasso Plattner Institute

Office: A-1.7/8

Tel.: +493315509-414

E-Mail: Anton.Krohmer(at)hpi.de

2020 [ nach oben ]

- Hyperbolic Embeddings for Near-Optimal Greedy Routing. Journal of Experimental Algorithmics (JEA) 2020

2018 [ nach oben ]

- Cliques in Hyperbolic Random Graphs. Algorithmica 2018: 2324-2344
- De-anonymization of Heterogeneous Random Graphs in Quasilinear Time. Algorithmica 2018: 3397–3427
- On the diameter of hyperbolic random graphs. SIAM Journal on Discrete Mathematics 2018: 1314-1334
- Unbounded Discrepancy of Deterministic Random Walks on Grids. SIAM Journal on Discrete Mathematics 2018: 2441-2452
- Efficient Embedding of Scale-Free Graphs in the Hyperbolic Plane. Transactions on Networking 2018: 920-933
- Hyperbolic Embeddings for Near-Optimal Greedy Routing. Algorithm Engineering and Experiments (ALENEX) 2018: 199-208
- Towards a Systematic Evaluation of Generative Network Models. Workshop on Algorithms and Models for the Web Graph (WAW) 2018: 99-114

2017 [ nach oben ]

- Phase Transitions for Scale-Free SAT Formulas. Conference on Artificial Intelligence (AAAI) 2017: 3893-3899
- Bounds on the Satisfiability Threshold for Power Law Distributed Random SAT. European Symposium on Algorithms (ESA) 2017: 37:1-37:15

2016 [ nach oben ]

- Hyperbolic Random Graphs: Separators and Treewidth. European Symposium on Algorithms (ESA) 2016: 15:1-15:16
- Efficient Embedding of Scale-Free Graphs in the Hyperbolic Plane. European Symposium on Algorithms (ESA) 2016: 16:1-16:18EATCS Best Paper Award

2015 [ nach oben ]

- Parameterized clique on inhomogeneous random graphs. Discrete Applied Mathematics 2015: 130-138
- On the Diameter of Hyperbolic Random Graphs. International Colloquium on Automata, Languages and Programming (ICALP) 2015: 614-625
- Cliques in Hyperbolic Random Graphs. International Conference on Computer Communications (INFOCOM) 2015: 1544-1552
- Unbounded Discrepancy of Deterministic Random Walks on Grids. International Symposium on Algorithms and Computation (ISAAC) 2015: 212-222

2014 [ nach oben ]

- De-anonymization of Heterogeneous Random Graphs in Quasilinear Time. European Symposium on Algorithms (ESA) 2014: 197-208

2012 [ nach oben ]

- Efficient Key Pathway Mining: Combining Networks and OMICS Data. Integrative Biology 2012: 756-764
- Efficient Algorithms for Extracting Biological Key Pathways with Global Constraints. Genetic and Evolutionary Computation Conference (GECCO) 2012: 169-176
- Parameterized Clique on Scale-Free Networks. International Symposium on Algorithms and Computation (ISAAC) 2012: 659-668

2010 [ nach oben ]

- RatFish: A File Sharing Protocol Provably Secure against Rational Users. European Symposium on Research in Computer Security (ESORICS) 2010: 607-625

# 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?