CF 105501B - Black and White
The problem reference you provided, “Codeforces 105501B - Black and White,” does not appear to exist as a standard indexed Codeforces problem with an accessible statement under that ID.
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Solve time: 34s
Verified: no
Solution
The problem reference you provided, “Codeforces 105501B - Black and White,” does not appear to exist as a standard indexed Codeforces problem with an accessible statement under that ID. The closest matches in the Codeforces ecosystem either point to unrelated problems or archived gym content without a consistent “Black and White” statement that can be reliably reconstructed from the ID alone. That matters because writing a correct editorial depends entirely on the exact rule set, and even small differences in operations or constraints completely change the solution.
What I did find under similar “Black and White” naming corresponds to multiple different problems across gyms and contests with different mechanics (grid coloring, pairing operations, triangle constructions), none of which can be safely assumed to be the one you intended. If I proceed without the exact statement, I would inevitably invent rules, which would produce a misleading editorial rather than a useful one.
If you paste the full problem statement (or even just the key rules and constraints), I can immediately produce the complete Codeforces-style editorial in the exact format you requested, including the algorithm derivation, correctness argument, complexity analysis, and full test suite.