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TheScrasse's blog

By TheScrasse, history, 14 months ago, In English

Sorry for weak tests in 1917C - Watering an Array.

Initially, the statement had the array b in input, and we had to do these three things simultaneously:

  • make O(n2) pass;
  • make O(nd) fail;
  • make d small enough (i.e., 106), so that the input could be read fast in any language.

But O(nd) was too fast, so (on Dec 22) we decided to use d109 and compress the array. But testers had already tested the old version of the problem, and I can't expect testers to reset their memory and retry the problem, so no one found the wrong O(nk) solution.

I'm sorry for making at least two mistakes:

  • Modifications 2 days before the contest may be ok, but they must be checked very carefully because fewer testers will see them.
  • I should have checked the existence of a pretest with all small cases. Maybe in this problem such test is not so comfortable to make, but you can achieve a similar effect by using a pretest with many random cases where every value in the input is small.

Please downvote this blog (instead of the announcement).

  • Vote: I like it
  • +515
  • Vote: I do not like it

| Write comment?
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14 months ago, # |
  Vote: I like it +146 Vote: I do not like it

Nobody can tell me what to do, upvoted😠

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14 months ago, # |
Rev. 2   Vote: I like it +41 Vote: I do not like it

Don't worry. Bro had a perfect Pinely Round 3 (Div. 1 + Div. 2), but ruined those guys contest by weak tests and FST scheme. ok

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14 months ago, # |
  Vote: I like it +107 Vote: I do not like it

> "Please downvote this blog"

> gets upvoted

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14 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Thank you for the systests. Farming +20 points of rating after systests and failing to solve B fast was enjoyable. You have nothing to apologize for.

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14 months ago, # |
  Vote: I like it 0 Vote: I do not like it

No worries, i thought about iterating up to n is not enough is not enough but during implementing this thought just disappeared.

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14 months ago, # |
  Vote: I like it +1 Vote: I do not like it

no problem , thanks for the contest

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14 months ago, # |
  Vote: I like it +1 Vote: I do not like it

no worries bro. you are doing great bro keep up the good work. div1 + div2 was extraordinary.

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14 months ago, # |
  Vote: I like it +22 Vote: I do not like it

After all, passing pretests does not guarantee that the solution is correct — as long as main tests are strong enough.

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14 months ago, # |
  Vote: I like it +1 Vote: I do not like it

Happened to me :( I thought my solution was AC and then system testing comes and I see WA on test 26. I've lost a lot of motivation from having bad performance on a couple rounds in a row

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14 months ago, # |
  Vote: I like it +3 Vote: I do not like it

Good new, that I didn't get FST on this problem.

Bad new, that I didn't AC-ed it during the contest.

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14 months ago, # |
  Vote: I like it +8 Vote: I do not like it

Unintensional weak pretest might be annoying but it also reminds us to prove our logic using methods other than "Proof by AC". The problems were nice.

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14 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Why downvote? I got tons of rating. After all, the main tests are fine.