My submissions to round 1 and 2 of the 37th Bundeswettbewerb Informatik (German computer science competition for school students).
Documentation, comments and most of the code of round 1 are in German of course, though the code for round 2 is in English. For the the actual problems and relevant material see the competition website.
https://bwinf.de/bundeswettbewerb/37/1-runde/
Done in Java. In short the questions boil down to:
Problem 1: Finding the universal sink of a social network graph.
Problem 2: Twisting and Untwisting texts where the middle letters of each word are scrambled.
Problem 3: Increasing the winnings in a game involving placing numbers.
https://bwinf.de/bundeswettbewerb/37/2-runde/
Done in Python. Basically about finding Euclidian Shortest Paths and using them to maximise the time someone can stay at home before leaving in the morning. However, the implemenation is far from efficient since the Visibility Graph needed for the solution is constructed using a Brute Force approach.
Credit for the problems, example material, etc. goes to the organisers of the competition obviously. This code and documentation for it: Tatiana Sedelnikov.