Literally, which is used to save some algorithm practices and useful code structures.
/codechef, all of its files come from CodeChef;
/codeforce, all of its questions come from CodeForce;
/gcj, its questions come from some practices of Google Code Jam;
/marathon, some questions come from Marathon match of Topcoder;
/srm, its questions come from Single Round Game of TopCoder;
/well-known-questions, some popular interview questions or famous algorithm questions.