You are thinking as of [row][column] and the solution is [column][row]

Managed to pass all tests except the last one wich exceeds time.

My solution creates the array and then it searches the array in O(n) but creating the array is a O(n^2).

I've seen the other discussions and you gave a hint to check "one step ahead", that the algorithm has to be O(log(n)) and that there can't be a data structure big enough to hold the seq[n] info.

I'm thinking maybe there is no need to create any data structure at all?

Maybe its a recursion of very few steps?

Can you shine a bit of light on me? Thanks, great problem, it's kept me thinking on it these last days