To be Honest Problems in HackerRank would definitely help you in clearing the online techinical test conducted by many top notch companies. Questions over there are more straight forward, short and precise, and which involves knowledge of well known algorithms.
Here are some most asked Hackerrank questions with solutions. Number of Islands using DFS. Subset Sum Problem. Rat in a maze problem. Number of ways to reach the nth stair. Sudoku problem. Rotate the matrix by K times. 0-1 Knapsack problem. Detect a loop in a linked list.
If you are not used to solving different kinds of problems, then it will appear hard. Hackerrank has around 5 levels of difficulty: Easy, Intermediate, Hard, Expert and Advanced. I suggest you pick a certain language and start with the warmup challenges to get used to the environment.
Overall, HackerRank is extremely useful for job applicants because it prepares you for the type of questions you will be asked during the technical stages of your interview. Most employers now use platforms like HackerRank to narrow down their candidate list so it allows you to get ahead