When you say you had to work harder to get the same result, do you mean the programming or the math? In my CS classes I saw really smart kids who were aces in the theoretical aspects of the program but couldn't grok programming. I also saw the reverse. You will have to be honest with yourself and figure out which kind of person you are and if you are willing to put in the necessary work to be 'big 4' material.
My advice, is keep practicing the algorithms, but do so with purpose. Try to tie in what you are learning with what you are doing at work, or a side-project. The essentials will osmose over time. Learning this stuff without having the proper context to understand is value is difficult ... (for me anyways).
At this point, I'm trying to assess what amount of work it's going to take to get into one of the "big 4"-type companies. I also need some way to feel like I'm improving.
1.5: Interviewing is like dating. At the end of the day, it's all about a mutual compatibility among you and the people you work with.
2: Interviews aren't things you study for. When I interview candidates, I'm trying to figure out if they can learn and if they understand core concepts that come with experience.
I must say this: I can tell when someone studies for my interview. They get all the questions "right," so then I start twisting the questions and the candidate starts acting like "you said this wouldn't be on the test." Those candidates are rejected.
In an interview, I can always take some code on the board, make up a funny situation that you didn't study for, and see how you handle it. If all you do is study interview questions from a book, these questions will tank you.
I've had two situations where a candidate who studied my interview made it past. In one case, the candidate was fired after a few months because he was too focused on goals that weren't our business's goals; and because the quality of his work sucked. In the other case... Well, let's just say that upper management is well aware of the problem.
Personally, I don't find it useful to perform a rote rehearsal of the material. I'd much rather be able to intuitively understand it because I hope it will help me in areas other than interviewing.