https://codeforces.com/recent-actionsCodeforces - Recent actions - Powered by AtomRSSAtomRSScontact@atomgroup.dev (AtomRSS)enMon, 19 Oct 2026 06:09:13 GMT5I can see why people hate grays. https://codeforces.com/blog/entry/157942?#comment-1400487https://codeforces.com/blog/entry/157942?#comment-1400487Sun, 18 Oct 2026 21:42:00 GMTI think weak samples on d2A might not be a great experience for new competitors going through WA hell or higher level people who just want to get to the later problems. (Also offtopic thing I'm not sure if I just have skill issue but for some reason I find it harder to prove my solutions on d2As than hard problems. I always feel uneasy when submitting but the samples have generally been strong enough to catch any implementation mistake and I haven't had my idea be wrong ever.) Otherwise I would probably agree and just say that deciding either way is more of a matter of the goal (like, "how important is it to us as authors that you see the edge case yourself")https://codeforces.com/blog/entry/157904?#comment-1400486https://codeforces.com/blog/entry/157904?#comment-1400486Sun, 18 Oct 2026 21:34:21 GMTThere is also an alternative solution to D2 that requires almost no thinking, although it has an extra $$$O(\log n)$$$ factor. SpoilerFirst, notice that we can always place new intervals such that no interval is strictly inside another. Second, we can binary search the number of new intervals.Let's see how to check if $$$k$$$ new intervals is enough. As in the editorial, do the XOR hashing and call it $$$h_1, \dots, h_n$$$. Now, process the hashes from left to right: if we haven't seen $$$h_i$$$ before, we can leave it as it is. Otherwise, we need to either open a new interval starting at the $$$i$$$-th position, or close an existing interval at the $$$(i - 1)$$$-th. But, as per the first observation, the choice is simple: if we haven't used $$$k$$$ new intervals, we create a new one, else keep closing the leftmost interval until we get a new hash.As a result, $$$O(m + n \log n)$$$ that passes with a little bit of constant optimization: 395112577.https://codeforces.com/blog/entry/157917?#comment-1400483https://codeforces.com/blog/entry/157917?#comment-1400483Sun, 18 Oct 2026 20:50:36 GMTblud got ragebaited :joy:https://codeforces.com/blog/entry/157904?#comment-1400482https://codeforces.com/blog/entry/157904?#comment-1400482Sun, 18 Oct 2026 20:36:41 GMTOn E, it is cool to think of the string as euler tour of the tree. Operation is then removing the leaf and creating new root for the tree.https://codeforces.com/blog/entry/157917?#comment-1400479https://codeforces.com/blog/entry/157917?#comment-1400479Sun, 18 Oct 2026 19:45:59 GMTI solved E like this, im trying to merge some run with some another run (of left brackets from left to right.) I keep a prefix sum of gain in longest length if i merge some runs (length of left run + length of right run — number of right brackets in between), then I use sparsetable to query the best answer for each run of left brackets building leftwards and I handle the first run of brackets differently since you dont lose a left bracket from an operationhttps://codeforces.com/blog/entry/157917?#comment-1400470https://codeforces.com/blog/entry/157917?#comment-1400470Sun, 18 Oct 2026 19:02:38 GMTUnusual Style Changes in Um_nik's Contributionhttps://codeforces.com/blog/entry/157772?#comment-1400468https://codeforces.com/blog/entry/157772?#comment-1400468Sun, 18 Oct 2026 18:59:57 GMTIn Problem D1 idk why i was trying to find the most optimal answer so bad that even though i got the solution, i was thinking that my solution is wrong and there must be a smaller number of sensor possible.https://codeforces.com/blog/entry/157917?#comment-1400462https://codeforces.com/blog/entry/157917?#comment-1400462Sun, 18 Oct 2026 18:41:15 GMTAbout example test caseshttps://codeforces.com/blog/entry/157904https://codeforces.com/blog/entry/157904Sun, 18 Oct 2026 18:28:21 GMTWorldQuant Round 1 (Codeforces Round 1128, Div. 1 + 2)https://codeforces.com/blog/entry/157538https://codeforces.com/blog/entry/157538Sun, 18 Oct 2026 18:26:41 GMTWorldQuant Round 1 (Codeforces Round 1128, Div. 1 + 2) Editorialhttps://codeforces.com/blog/entry/157917https://codeforces.com/blog/entry/157917Sun, 18 Oct 2026 18:25:33 GMTa free extension to highlight, draw and take notes on CF problemshttps://codeforces.com/blog/entry/157938https://codeforces.com/blog/entry/157938Sun, 18 Oct 2026 17:03:42 GMTThe coordinators of that round where he was accused to be cheating confirmed that he deserve the ban.https://codeforces.com/blog/entry/157657?#comment-1400440https://codeforces.com/blog/entry/157657?#comment-1400440Sun, 18 Oct 2026 15:55:03 GMTAs a tester, i tested really bad.https://codeforces.com/blog/entry/157933?#comment-1400432https://codeforces.com/blog/entry/157933?#comment-1400432Sun, 18 Oct 2026 14:59:23 GMTFinal Round Announcement: Path to Mastery (A&DS-1 and A&DS-2)https://codeforces.com/blog/entry/157933https://codeforces.com/blog/entry/157933Sun, 18 Oct 2026 14:54:53 GMTHi! There is no filter based on whether you might be able to solve the problems. Contest announcements are filtered only by the division's rating limit. Div. 3 announcements go to users rated below 1600 and to unrated users, and Div. 2 announcements go to users rated below 2100. Rounds open to everyone, such as Div. 1 + Div. 2 and Educational rounds, go to all subscribed users. Your account qualifies for all of them, and your "Contest email notification" setting is on (it's on by default).We checked our mail server (Postfix) logs for your address. There are eight deliveries: September 21, 24 and 25, and October 6, 9, 11, 13 and 15. That is every contest announcement sent since September 20, including Codeforces Round 1125 (Div. 3) and WorldQuant Round 1. Every one of them is logged as status=sent (250 2.0.0 OK) from gmail-smtp-in.l.google.com, so Google's mail server accepted them all. Nothing for you is waiting in our queue now. Logs older than about September 20 have already been rotated, so we can't check the August announcements. Our mailing system keeps per-recipient records only for the two latest campaigns, so for older ones the server logs are the only source.Gmail accepting a message doesn't guarantee it reached your Inbox. Most likely the announcements are in your Promotions or Spam folder. If you find one there, mark it as "Not spam" or move it to Primary so future ones arrive normally. Some other providers, such as Microsoft and Apple, are currently rejecting part of our mail because of a blocklist issue, but that doesn't affect Gmail: it accepted all of your messages.https://codeforces.com/blog/entry/157538?#comment-1400428https://codeforces.com/blog/entry/157538?#comment-1400428Sun, 18 Oct 2026 14:54:52 GMTits called queueforces, it happens regularly and we just have to live with ithttps://codeforces.com/blog/entry/157919?#comment-1400416https://codeforces.com/blog/entry/157919?#comment-1400416Sun, 18 Oct 2026 14:30:49 GMTFair point! A good prompt covers the hints. The skills just save you from rewriting it every time and keep it consistent: /structure and /techniques list candidates without saying which one works. /input gives edge cases with outputs computed by running a brute force, not guessed. If you paste your code, it runs a stress test and shows the counterexample instead of rewriting your solution. So it's less "a better prompt" and more a prompt that can also run and verify code.https://codeforces.com/blog/entry/157908?#comment-1400411https://codeforces.com/blog/entry/157908?#comment-1400411Sun, 18 Oct 2026 14:14:10 GMTSubmission in queue problemhttps://codeforces.com/blog/entry/157932https://codeforces.com/blog/entry/157932Sun, 18 Oct 2026 13:39:15 GMT