I was solving this problem and after I solved it by myself I decided to implement editorial's solution. Strangely my first submission was really slow 55982450, but after changing the order of dimensions it got 5x faster 55999256.
I was solving this problem and after I solved it by myself I decided to implement editorial's solution. Strangely my first submission was really slow 55982450, but after changing the order of dimensions it got 5x faster 55999256.
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There was a blog before where that happened before, and the reason was because of cache. When storing a multi-dimensional array in a more cache-friendly order, you will get better performance.
I've noticed this specifically for sparse tables. Having st[j][i] store the 2^j-th ancestor of i is an order of magnitude faster than st[i][j].
Nice one, I've never thought about this before. It makes sense. I will consider this next time I implement sparse table.