cgy4ever's blog

Topcoder SRM 715
By cgy4ever, history, 8 years ago, In English

Topcoder SRM 715

Time: 9:00 pm EDT Tuesday, May 30, 2017

Calendar: https://www.topcoder.com/community/events/

  • Vote: I like it
  • +21
  • Vote: I do not like it

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8 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Holy Mike and Mother of TopCoder! Schedule announced up to end of May!

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    8 years ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    We will announce TCO schedule (online and regionals) very soon — it will be up to September. :P

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    8 years ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    Yes but only 2 rounds a month, how I miss the old days when there were 4 rounds every month :(

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8 years ago, # |
  Vote: I like it +19 Vote: I do not like it

Starts in 1 day.

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    8 years ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    Another reminder because participation in rounds at this time is very less.

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8 years ago, # |
  Vote: I like it +31 Vote: I do not like it

What was the point of making div1-250 incredibly easier than usual?

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    8 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    To test people's speedcoding / give randoms a chance to beat reds :)

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8 years ago, # |
← Rev. 2   Vote: I like it +37 Vote: I do not like it

I was the writer for this round. Here is the code and some short explanations.

div2
div1
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    8 years ago, # ^ |
      Vote: I like it +11 Vote: I do not like it

    You were also the writer for the last 2 contests(w/o this SRM) I participated in :O

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8 years ago, # |
  Vote: I like it +20 Vote: I do not like it

How to solve hard? I thought that if the solution is not unique (if it exists) then it will be kinda hard to check it. So I wrote some bruteforce with breaks hoping that bad branches will be very short. And it passes.

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    8 years ago, # ^ |
    ← Rev. 2   Vote: I like it 0 Vote: I do not like it

    You can see div2 hard on how to check (in essence, you know the root from pre and post, and the in order traversal tells you how to split into left and right subtrees).

    I'm not sure if it's possible to break a solution like yours.

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      8 years ago, # ^ |
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      I'm stupid, yeah. I use all that ideas in my bruteforce :)

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    8 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Haha also thought about some kind of backtracking hoping it will crash shortly :P. But too late in the contest :<.

    Actually checking if solution is good is pretty easy. I tried to solve problem recursively and in every execution I was given two orders and two types, but that didn't suffice to make good transitions. But if you are given three orders and three types then you always know what is the root (because you are given both preorder and postorder and can take first/last one in those), what belongs to left subtree and what belong to right (because you know where is root in inorder), so you can proceed recursively and recover whole tree in unique way.

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8 years ago, # |
← Rev. 2   Vote: I like it +57 Vote: I do not like it

Div1Easy : competitive typing
Div1Med : no clue
We in range 1400-1500 need an intermediate.

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    8 years ago, # ^ |
      Vote: I like it +37 Vote: I do not like it

    I had the following problem when I was an admin:

    D1 Easy shouldn't be too hard. Otherwise many people will get zero.

    E ≤ 1500

    D1 Hard shouldn't be too hard. Otherwise targets will get bored.

    H ≥ 3000

    The difference between Easy and Medium should be small. Otherwise intermediate people will get bored.

    M - E ≤ 700

    For the same reason, the difference between Medium and Hard should be small.

    H - M ≤ 700

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      8 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Infeasible (´；ω；｀)

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      8 years ago, # ^ |
        Vote: I like it +5 Vote: I do not like it

      What is E, H, M? The rating that have 50% chance to solve?

      Btw, do you remember why we wanted to set about 1% solve rate for Div1-Hard? (Even bmerry told me that Div1-Hard is unsolvable in recent years, so I'm thinking about lower the difficulty.)

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        8 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        Please don't take the values very seriously, I just wanted to say that it's very hard to find a problemset that suits everyone.

        If my memory is correct, CF changed the cutoff between D1 and D2 a few years ago. I think if TC do the same (without changing the difficulties of problems) the situation becomes better. For blue coders D2 Hards look very suitable (they are somewhere between d1 easies and d1 mediums).

        I don't remember about 1% rate, but that can be outdated given that recently only around 300 people participate in D1 and still lots of very strong people participate. Now I think anywhere between 1 person and 5% is suitable.

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        8 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        Btw why cant topcoder have more problems in a round? Even 1 extra problem would help decrease the massive jumps in difficulty.

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          8 years ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          You think the system and the applet are designed enough extensible and tough so that it's possible?

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            8 years ago, # ^ |
              Vote: I like it +25 Vote: I do not like it

            Maybe not. But IMO, topcoder is losing popularity and they have to do something about it before its too late.

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              8 years ago, # ^ |
                Vote: I like it 0 Vote: I do not like it

              I relay think so too :,(

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    8 years ago, # ^ |
      Vote: I like it +9 Vote: I do not like it

    I have 1800 and it's the same for me. Solve easy in 10 min and go AFK — that's my typical round. I stopped competing at Topcoder because of that.

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      8 years ago, # ^ |
        Vote: I like it +5 Vote: I do not like it

      I agree. I have 1799 in Topcoder, but last time (SRM 714), I solved easy in 4 min but I can't solve medium.

      What I feel strongly recently is "Div1-Med difficulty is increasing".
      The SRM 715-710 Med solved are 20, 45, 22, 2, 107, 6. (Average numbers of competitor is about 270)
      But SRM 515-510 Med solved are 57, 39, 159, 67, 173, 32. (Average numbers of competitor is about 600)

      So, I think people who rating is 1500-2200 can solve easy rapidly, but can't solve medium especially Div1-Med's solved is 1-digit.

      Recently, I'm practicing in Div1-Med. If I could gain performance to 2000+,... but I couldn't solve Div1Med and I would be sad in contest that Div1-Med's solved is 1-digit.

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8 years ago, # |
  Vote: I like it 0 Vote: I do not like it

wow, it's my first srm, and the result is no too bad, just learn and try.

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8 years ago, # |
← Rev. 2   Vote: I like it +10 Vote: I do not like it
ICPC WF spoiler (do not open unless completely sure)
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