TheScrasse's blog

Sorry
By TheScrasse, history, 4 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 $$$O(n^2)$$$ pass;
  • make $$$O(nd)$$$ fail;
  • make $$$d$$$ small enough (i.e., $$$\leq 10^6$$$), 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 $$$d \leq 10^9$$$ 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

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4 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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4 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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4 months ago, # |
  Vote: I like it +107 Vote: I do not like it

> "Please downvote this blog"

> gets upvoted

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4 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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4 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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4 months ago, # |
  Vote: I like it +1 Vote: I do not like it

no problem , thanks for the contest

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4 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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4 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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4 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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4 months ago, # |
← Rev. 3   Vote: I like it -22 Vote: I do not like it

Hope to get better

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4 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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4 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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4 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.

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