I have given the phone interview and am waiting for the onsite interview. The phone interview consisted of one problem. I had to sketch the solution and write code in a shared Google Doc. I wrote code for it in C++.

During the whole time, I explained what I was doing because that was the most important part. As there is no compilation, neither you nor your interviewer will know for sure if it is correct. However, the important part is that there is no bug that you or your interviewer can see. If your interviewer sees something that might not be correct, they will give you hints towards fixing it. It's actually more like a collaboration to solve a problem rather than you single-handedly solving it.

There is a frog at position 0 on the side of a river.

Positions [1...L-1] are inside the river. Position L is the other side.

There are some rocks at specific positions in the river. At each rock or side of the river, you can only go in the forward direction.

You have a speed. Currently, your speed is 0. From your current position, you can either increase your speed, keep the same speed, or decrease your speed. You can reach the next rock if the difference between your position and that rock is the same as your speed. You can reach the other side if you can reach position >= L. You don't necessarily have to land on position L.

You have to return if it is possible.