General - (AFAI can see) Hamler does not support streams/lazy lists (yet). Means for this one I will not use a data structure based approach, but will compute the solution :).

For that we will read the input and will build and array of lines that have the tree positions on it (let's call it a forrest).

I can then go into that forrest with my current position (x, y) and can check, if I am hitting a tree. Note: y needs to be modolo the line length.

Then I am repeating this n times (the number of lines in the input file) advancing m steps (3) to the right until I am done (and count the number of trees I am hitting on the way).

Part 1 - Doing the above.

Part 2 - Using part1 to do it for all given moves.