[anonymoushn]

There is a common set of algorithms that most people who do well in such a contest can implement whenever they like, but most of the effort involved in solving the problems happens before they write any code, and many (half or more?) problems can't be solved by just applying the techniques from this repertoire.

[baobabKoodaa]

This is correct. A typical CodeForces problem is intentionally constructed as a unique snowflake that can't be solved by just calling a library function. You need to be able to design an algorithm that solves that specific unique snowflake on the spot. Perhaps your algorithm also makes some library calls to other algorithms in your comp.coding library, but those are merely building blocks for your own thing, which you have to invent.