Let $A$ be a square non-singular matrix. Moreover, $A_{ij} = 0$ for every $i> j+1$ , meaning that in every column, from the elements that are under the diagonal, only the first element under the main diagonal is not zero.
The task is to find an efficient method to solve $Ax = b$.
I don't really have any idea, besides to use Gaus' eliminations as always. I think it will take $O(n^2)$
I can't think of anything better.
Help would be appreciated.