Explanation for the mathematical solution of atcoder problem E — Σ[k=0..10^100]floor(X/10^k)

Revision en3, by Omar_Hafez, 2022-05-28 12:35:44

Hello codeforces, I solved This problem from atcoder with the "Obvious" brute-force solution which is O(N). But when I take a look at the editorial I found a Beautiful mathematical solution that solves it in O(1) O(N) but with a lower constant factor, use lower memory and easy beautiful code. But unfortunately, I didn't understand it so Can anyone please explain it to me?

I really appreciate any help you can provide.


  Rev. Lang. By When Δ Comment
en3 English Omar_Hafez 2022-05-28 12:35:44 97 Tiny change: 'ves it in O(1). \nBut un' -> 'ves it in <strike>TO(1)</strike>T. \nBut un'
en2 English Omar_Hafez 2022-05-27 21:49:07 5
en1 English Omar_Hafez 2022-05-27 21:48:12 553 Initial revision (published)