This problem is supposed to be an straightforward application of a set data structure. Regardless of what language you are using there is probably a data structure in its standard library (probably called something close to set) that supports inserting and checking if an element is in it. To solve this problem you should learn how to use it and use it.
This is also supposed to be a straightforward application of a data structure, but of a map/dictionary/symbol table. First insert the input into the data structure using the words as keys and the values as a count of their frequency, and then go through the input again to tally up the points. To solve this problem you should learn how to use the default map/dictionary/symbol table data structure from your favorite programming language and then use it.
Another problem for you to learn how to use a data structure: a queue. To solve it you have to simulate this process, by keeping track of the current time:
This problem is an implementation problem, you don’t need to think too much about it. You have to implement a data structure that looks like a stack (so you can see the most recent conversation on the screen and add new conversations if there are less than k), but where you have arbitrary access to any element (so you can swap and shift).
This is the most challenging problem and uses a technique that is not usually super well-known called difference arrays. Make sure you know how it works first (here is an article about it). Then to apply it to this problem you have to do it twice, once to each of the m operations, and then you have to use a “difference array of difference arrays” approach to apply each one of the k queries. It’s a bit tricky, but it’s very worth it once you solve it.
ACM Student Chapter of Princeton, Inc