They are always the same questions.

The first question is to list the data structures you know. The answer is: Array, List, Heap, Queue, Stack, Hash, Tree, Graph.

The second question is how a queue and stack work. My answer is FIFO, FILO.

The third question is to describe the difference between an array and a list. My answer is: an array has a fixed size, and a list is dynamically allocated. An array provides direct access. A list accesses data sequentially from the first element.

The fourth question is how a hashmap works. Take an example of how to use it. My answer is: a.put("name", "123456"); // key is "name", value is string "123456".

The fifth question is to group strings that appear in many brackets. I don't fully understand this question. Many people say the answer is a hashmap, but it seems there might be better answers. I don't know.

Then, I heard other people being asked to write a binary tree, how virtual functions work in Java, and how to delete duplicates in an N-size array where each element is from 1 to N.

That's what I know about Blackrock. Their questions do not change. I hope everything goes well for you, guys!

The fifth question asks you to group strings that appear in many brackets. Actually, I don't understand this question very well. Many people suggest the answer is a hashmap, but there seem to be better options.