K1o0n's blog

Codeforces Round #957 (Div. 3)
By K1o0n, 2 years ago, translation, In English

Hello, Codeforces! We are pleased to invite you to Codeforces Round 957 (Div. 3), which will be held on Jul/11/2024 17:35 (Moscow time).

The round will be hosted by rules of educational rounds (extended ICPC). You will be offered 7 problems, which I with Noobish_Monk, ErnKor, Kmes and ArSarapkin have prepared for you.

The rules of the third division are:

  • The penalty for a wrong submission is 10 minutes.

  • 12-hour phase of open hacks after the end of the round (hacks do not give additional points)

  • after the end of the open hacking phase, all solutions will be tested on the updated set of tests, and the ratings recalculated.

Reminding you, that only trusted participants of the third division will be included in the official standings table. This is a forced measure for combating unsporting behavior. To qualify as a trusted participant of the third division, you must:

  • take part in at least five rated rounds (and solve at least one problem in each of them),

  • do not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600 (or you are a newcomer/unrated), then the round will be rated for you.

We would like to thank everybody, who helped in preparing this round:

Good luck!

UPD1 After the end of the round, Shayan will broadcast the solutions, a recording will also be available, but we will also prepare a textual editorial.

UPD2 Video Discussion by Shayan

UPD3 Video of solving the round + Editorial by the "winner" of this round, neal

UPD4 Editorial.

UPD5 Congratulations for the winners:

Official:

  1. thegoat

  2. shil_pelmen

  3. xiojoy

  4. _duskTempest

  5. LargeRice

Official + Unofficial:

  1. tourist

  2. neal

  3. Dominater069

  4. abc864197532

  5. hitonanode

  • Vote: I like it
  • +187
  • Vote: I do not like it

Comments Comments (195)
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2 years ago, hide # |
 
Vote: I like it +15 Vote: I do not like it

cool

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2 years ago, hide # |
 
Vote: I like it -16 Vote: I do not like it

my goal to reach +1700 after this round

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

__ combating unsporting behavior. To qualify as a trusted participant of the fourth division, you must: __ take part in at least five rated rounds (and solve at least one problem in each of them), __ do not have a point of 1900 or higher in the rating. __ Regardless of whether you are a trusted participant of the fourth division or not, if your rating is less than 1600 (or you are a newcomer/unrated), then the round will be rated for you.

why is it fourth division

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2 years ago, hide # |
 
Vote: I like it +10 Vote: I do not like it

Finally I can write this: my first unrated div3 :D

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

As a tester of this round, I will say that the tasks were interesting

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2 years ago, hide # |
 
Vote: I like it +14 Vote: I do not like it

Just curious: How do you guys propose a Div3 contest?

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2 years ago, hide # |
 
Vote: I like it +2 Vote: I do not like it

Hoping we all get positive delta :)

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2 years ago, hide # |
 
Vote: I like it +17 Vote: I do not like it

As a tester i confirm that problems are indeed cool and worth solving.

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2 years ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

finally a div3 after a long time.

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

Can you tell me how to propose div3 contests? Vladosiya, Gornak40 ?

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2 years ago, hide # |
 
Vote: I like it +13 Vote: I do not like it
Vladosiya for deleting the lore in almost all of the problems...

Thank you.

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

f(n)=(n−1)⋅(f(n−2)+f(n−1))

can we solve this eqn using matrix expo???

if yes then plzz give me the matrix...

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2 years ago, hide # |
 
Vote: I like it +11 Vote: I do not like it

I like the monk's organization :D

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

I want to go specialist, Good luck for me

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2 years ago, hide # |
 
Vote: I like it -14 Vote: I do not like it

Shayan streams pretty much in recent month for problems' solution. I appreciate him a lot.

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2 years ago, hide # |
 
Vote: I like it +17 Vote: I do not like it

As a tester, I can guarantee that the round will be interesting!

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2 years ago, hide # |
← Rev. 3  
Vote: I like it +9 Vote: I do not like it

I want to solve 3 questions in this contest :)

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2 years ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

How to be tester? Is this random?

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    2 years ago, hide # ^ |
     
    Vote: I like it +2 Vote: I do not like it

    No, it's not random. Most testers are friends of setters or coordinators. Yes, there are some "random" testers if you want to say it like that, but in a way that they are friends of friends.

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

As a problemsetter, good luck, guys!

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2 years ago, hide # |
 
Vote: I like it +10 Vote: I do not like it

As a tester of this round, I can say that this round will probably lower your rating, but the tasks are worth solving <3

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

a general doubt, penalty gets applied after correct submisson or doen't depend on correct submission?

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2 years ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

time to lock in

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

I hope I'll be +1300 after this round! Good luck to everyone!

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2 years ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

Looking forward to getting my first color today!

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

will trusted participant be rated ??

or just be included in the official standing ?

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    2 years ago, hide # ^ |
    ← Rev. 4  
    Vote: I like it +6 Vote: I do not like it

    Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600 (or you are a newcomer/unrated), then the round will be rated for you.

    If the rating range is 1600-1900(didn't cross 1900 at any time), then you would only be in the official standings.

    Btw, Congrats!! on reaching Expert

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

I hope to go forward and wish for this to be the best Div3. Odin is with us!!!

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

that went a bit better than last div2 (emphasis on a bit because i somehow crashed my ide 4 times which lost me about 4-6 minutes from E-G)

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

got stuck on F , ughhhhhhhhhhhhhhh.

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

Overall very nice problems and good contest. My first time solving E and hopefully I get a good delta :)

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

    is it just brute force ? 1e4*1e4 *100 it should not pass obviously

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      2 years ago, hide # ^ |
       
      Vote: I like it +1 Vote: I do not like it

      here's an oberservation: n*a-b can only be at most 7 digits which means b can only have at most 7 values for each a

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

      well nope, brute force is TLE, its basically going over all values of A (10^4 iterations) and the it is guaranteed that the length of a valid string after removing b bits from it will never exceed a length of 7 (cuz the constraints come into play) so for every A , you run 7 inner loops and then obviously you can find b in constant time using a formula.

      270014350

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        2 years ago, hide # ^ |
        ← Rev. 2  
        Vote: I like it +1 Vote: I do not like it

        you can also solve this with math i believe — start with an empty string (denoted as s), add the digits of n one-by-one to it, then solve the system of equations:

        (int)s = n * a - b

        numdigits(n) * a - b = numdigits(s)

        270034846

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

          ohh, thanks for this :) . During the contest, i was constantly trying to think in this direction cuz this is much more efficient than what i wrote but yeah my brain just didnt work. Thanks for the soln, appreciated.

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

C is the easiest but it was the hardest for me to write

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

ignore this was my worst performance soo far

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

How to solve F?

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2 years ago, hide # |
 
Vote: I like it -16 Vote: I do not like it

I literally cannot believe on how ChatGPT unable to solve stupid implementation problem like D.

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2 years ago, hide # |
 
Vote: I like it -8 Vote: I do not like it

Hi All, can anyone help me understand why I am getting memory limit exceeded on problem D? this is my submission, I followed a recursive approach to explore possible options of jumping and swimming, I am not using an extra data structure, thank you in advance for your help!

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2 years ago, hide # |
← Rev. 2  
Vote: I like it +11 Vote: I do not like it

Was it only for me ,or it was really hard to decode the problems?

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2 years ago, hide # |
 
Vote: I like it +2 Vote: I do not like it

Another round dusted by Indian cheaters.

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2 years ago, hide # |
 
Vote: I like it +5 Vote: I do not like it

Me staring at E for 1hr +

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

My brain got blown away after reading E was like another level for me.DIV3's have become harder now

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2 years ago, hide # |
 
Vote: I like it +72 Vote: I do not like it

Sharing my video of winning* the contest: https://www.youtube.com/watch?v=9Vv2ZukG1CM&t=2476s

(*tourist doesn't count)

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

Missed E, and actually missed the first time that I could clear Div3.

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

Ahh, D was so straightforward but I spent like an hour debugging just to get AC in 3 minutes after reimplementing my idea.

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

What is the thing you have to notice to solve E?

The only way I would be able to solve (I didn't do this) would be to precompute all of n from 2 to 100 and then have a python program just return those precomputed solutions...

How do we solve for B given we check for values of A... Maybe I wasn't on the right track at all for optimal solution though...

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

    Notice that B is also bounded by 10000, so the length of good results is bounded by len(10000*100-1) = 6. So you can simply iterate all strings of length 1-6 for each A

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2 years ago, hide # |
 
Vote: I like it +2 Vote: I do not like it

Easier than recent div4 round!

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2 years ago, hide # |
← Rev. 4  
Vote: I like it +57 Vote: I do not like it

The problems were great, but the confusing statements ruined it for me, I really think more attention should be given to making the statement clear and understandable.

For example in problem D it was not clear that k was for the entire problem, when I read it I thought he could not swim a distance more than k in a row which led to me writing a completely different solution and wasted a lot of time on this.

I spent more time understanding the problems than solving them.

I am not saying the contest is bad, but I felt this should be addressed.

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    2 years ago, hide # ^ |
    ← Rev. 2  
    Vote: I like it +3 Vote: I do not like it

    Same, initially i also thought it should be k consecutive rows. Luckily i decided to read samples where answer is NO and one of the test case explained where K need not be in a row

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    2 years ago, hide # ^ |
    ← Rev. 2  
    Vote: I like it +4 Vote: I do not like it

    I think you just misread they wrote that k is for the entire swim from 1...n

    The river is very cold. Therefore, in total (that is, throughout the entire swim from 0 to n+1 )

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    2 years ago, hide # ^ |
    ← Rev. 2  
    Vote: I like it +1 Vote: I do not like it

    Worst Problem was D . First time i solved so poor in DIV3 .

    The first line of each test case contains three numbers n,m,k(0≤k≤2⋅105,1≤n≤2⋅105,1≤m≤10) — the length of the river, the distance ErnKor can jump, and the number of meters ErnKor can swim without freezing.

    I read n then m then k and hence exchanged k's constraint with m's constraint . Stucked in the whole contest for more than 1 hour while solution is correct.

    https://codeforces.me/contest/1992/submission/270048258

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    2 years ago, hide # ^ |
     
    Vote: I like it +1 Vote: I do not like it

    same

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    2 years ago, hide # ^ |
     
    Vote: I like it +28 Vote: I do not like it

    i mentioned this issue in testing, but unfortunately they did not take it into account

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

    Actually I also choked because of this , but I also confused about the fact that how to solve this if the task is to compute if swimmer can swim the river if he can continously swim for only k units
    . Please explain you solution for this above wrongly interprated question . Thank you

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

      If you are asking about my solution if you could swim for at most k meters continuously, Here is what I tried to do (Not sure if it's correct or not)

      I used a prefix sum array to count the number of crocodiles, there is a crocodile between l and r if pre[r] - pre[l - 1] > 0

      I used a variable to store where the last log was, If there is water at the current index I check if the distance between it and the last log + m is less than or equal k and that there is no crocodile between log + m and the current index then the current index is reachable.

      The rest is similar to the solution of problem D

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2 years ago, hide # |
 
Vote: I like it +2 Vote: I do not like it

There are so many similar solutions for problem D which have been taken from youtube. They all have just changed variable names while initialising a variable name with m-1 and incrementing a variable if there is water and using some other variables and at last they are checking if variable value is not zero then print yes else no. Loads and Loads of solution in the same format, I had a brainrot seeing 10k+ submissions for D itself.

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

I might have gotten E in contest time itself but cloudflare had other plans.

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

Am I really dumb as from submission its looking like D is easy but I was not able to solve it

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

    D was ezz, not 10K easy tho :)

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

      Yeah 5k submission I can understand as I am dumb but 10k is just crazy I am getting -ve delta for sure :(

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

        well cheaters ruin it for actual hard-workers and thats pretty pathetic, like when i was giving div 3's 7-8 month ago and i was rated 900, if i solved 3 i would surely get +ve, but now its sort of impossible, either you get till E to get +ve or else you get fcked

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2 years ago, hide # |
 
Vote: I like it +7 Vote: I do not like it

bruh i asked chatgpt to solve D with dp and it actually worked

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

how brute-force round ，I love it.

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2 years ago, hide # |
← Rev. 3  
Vote: I like it +5 Vote: I do not like it

Please report this guy. He is sharing answer during the contest time. He is destroying the cp environment. here is the link : https://www.youtube.com/live/frrrP-SHXWA?si=nnX4Ghj0bqvDJEeN

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2 years ago, hide # |
 
Vote: I like it +10 Vote: I do not like it

Fantastic round! E was an amazing problem! Thanks a lot for the round Noobish_Monk ErnKor Kmes ArSarapkin and all testers!

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2 years ago, hide # |
 
Vote: I like it -16 Vote: I do not like it

there is a question in cf round 957 div3 just completed question no. E Novie Mistake if n==1 for a=3 and b=2 means string is empty value of n*a-b=1 but string is empty means it is zero it is not matching then why question consider string is empty as 1 and it didn't mention anywhere

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2 years ago, hide # |
← Rev. 4  
Vote: I like it +6 Vote: I do not like it

D has a very clean DP solution.

Let $$$dp[i]$$$ denote the minimum number of swims required to reach index $$$i$$$. The transitions are -

For $$$j = i + 1 - m$$$ to $$$i$$$

  • $$$dp[i + 1] = min(dp[j], dp[i + 1])$$$, if $$$s[j] =$$$ 'L'

$$$dp[i + 1] = min(dp[i] + 1, dp[i + 1)$$$, if $$$s[i] =$$$ 'W'

Finally, the answer is YES if $$$dp[n + 1] \le k$$$.

Submission Link: https://codeforces.me/contest/1992/submission/270032188

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    2 years ago, hide # ^ |
     
    Vote: I like it +6 Vote: I do not like it

    Yeah, that's true, but I exceeded the memory limit during the contest using dynamic programming, so I used BFS instead. It is also an easy solution.

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    2 years ago, hide # ^ |
    ← Rev. 3  
    Vote: I like it +8 Vote: I do not like it

    there is also easier greedy solution using O(1) extra memory: create a variable last_land_point and set it = i whenever you get on the land. Then if ever last_land_point become too far, that is farther than jumping distance, start incrementing a variable for how much to swim. If you hit a crocodile while swimming, not possible. If you have to swim too much, not possible.

    Code: https://codeforces.me/contest/1992/submission/269973081

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

    Hi, I struggle with tabulation DP, can you share any resource from where I can improve ?

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

      Tabulation DP is pretty much the same as recursive DP, you just have to calculate the DP values in the correct order, that is, the current state being calculated should not depend on a future state. Honestly the best way to learn tabulation DP is to solve more problems, CSES DP section the Atcoder DP contest helped me a lot.

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2 years ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

I submitted almost correct solution for E during the contest https://codeforces.me/contest/1992/submission/270016302, the only thing I didn't figured out was to convert to long long instead of size_t in the only place to avoid overflow. So disappointed, I will NEVER use any integer types except long long in competitive programming again!

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

// Can anybody tell me what's wrong in this implementation of D , I have chosen a variable pos to see if it is possible to pass the river and p tells if we found a "log" , c tells us if i found a "crocodile" and "w" tells us swimming through water i have as usual checked if if it is possible to get to a log then go there otherwise increase the position by m and check if there is one segment to swim to otherwise if only crocodiles were found btw i and i+m segment make pos false.





signed main() {
    ll t;
    cin >> t;
    while(t--) {
     ll n,m,k;
     cin >> n >> m >> k;
     string s;
     cin >> s;
 
    ll i = -1;
    bool pos = true;
    while(i<n){
        bool p = false;
        bool c = false;
        bool w = false;
      for(ll j = m;j>=1;j--){
          
        ll k = i+j;
        if(i+j<n){ 
            if(s[k]=='L'){
            // cout<<i+j<<endl;
            i = k;
            p=true;
            break;
         
        }
        if(s[k]=='C'){
            c = true;
        }
        if(s[k]=='W'){
            w = true;
        }
 
        }
        else{
            i = n+1;
            break;
        }
      }
 
      if(p==false and w==true){
          i+=m;
        if(i>=n){
            break;
        }
        else if(s[i]=='C'){
            pos = false;
            break;
        }
       else if(k>=1){
            // cout<<i<<"water1"<<endl;
            i+=1;
            k = k-1;
            // cout<<i<<"water"<<endl;
        }
        else{
        pos = false;
       break;
        }
      }
      else if(p==false and c==true){
        pos =false;
        break;
      }
    }
 
    if(pos){
        cout<<"YES"<<endl;
    }
    else{
        cout<<"NO"<<endl;
    }
    
      
         
 
  
}
}
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    2 years ago, hide # ^ |
    ← Rev. 2  
    Vote: I like it +5 Vote: I do not like it

    With this number of if-else-s and no proper indentation, it's hard to get the idea implemented right. The right thing to do is perhaps not to find a particular bug, but to take a step back and observe what can be changed globally. Consider developing these habits:

    • formatting the code to aid in implementation (any decent IDE has a keyboard shortcut for that)

    • thinking about solutions with as little if-else-if-if-else... forests as possible

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2 years ago, hide # |
← Rev. 3  
Vote: I like it 0 Vote: I do not like it

Never thought i will get 4 wrong submission on Div3-A :(

However solved B,C easily but spent too much time on D and didn't got much time to solve E Seems lots of people solved D so i might get -ve delta

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

    I think you will reach pupil easily because you didn't participate in too much contests I participated in more contests so I would be relieved if I got those +50

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2 years ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

Weird statements for D and F

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

Does anyone know what the error-"Invalid use of deleting symbols" mean? Here's the link for reference 270073853

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2 years ago, hide # |
 
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I'm sure many people brute forced the answers of E, and just made if and else cases of it, there weren't many numbers and was fairly easy to make cases for each n.

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    2 years ago, hide # ^ |
     
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    yeah since you really only have around 50 thousand cases (optimally) and it wouldn't be very hard to just bash out all the possible cases of a and b.

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

      No that would give TLE, I meant people brute forced the answers beforehand, and made if else cases like: if (n==2) cout << 3 << endl << x1 << x2 << endl .. ... if (n==3) ....

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        2 years ago, hide # ^ |
         
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        why would that give TLE? i did just that

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

        Personally, I believe that it shouldn't give TLE, due to the extra second it provides for the time constraints, 3 seconds, compared to 2 in B, C, D and 1 in A. I believe it should be possible to optimize enough to fit in the time limit, as 50,000 cases really isn't all that much in computing. You do have a point though.

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          2 years ago, hide # ^ |
           
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          You are missing the factor of building the number by getting individual digits which is atleast 20 operations for each i from 1 to 10^4. So your total operations would be 10000*5*20 for each test case, so a total 10^8 operations, I personally wouldn't risk on such a solution passing the TL.

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            2 years ago, hide # ^ |
             
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            one could easily optimize this by precomputing the number of digits that u will need and build the number from there. since that number is quite small it will not TLE

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            2 years ago, hide # ^ |
             
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            I'm not sure where you're getting these numbers from. Other than the $$$n = 1$$$ case (which has $$$9999$$$ possible answers, since $$$a = b + 1$$$ always works), among all $$$2 \le n \le 100$$$ there are a total of only $$$24$$$ other $$$a, b$$$ pairs actually possible. Precomputing all these and using if else statements would definitely not TLE.

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2 years ago, hide # |
 
Vote: I like it +12 Vote: I do not like it

really nice contest, I enjoyed the surplus of math-related questions, and it felt fitting for div 3. great job to all the organizers!

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2 years ago, hide # |
 
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Can someone help me why my submission give a wrong answer in problem F 270081629

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2 years ago, hide # |
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Enjoyed while solving the problems. But descriptions were just too bad. It took much time to understand each problems. Please make descriptions easy so that everybody can understand the questions easily

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2 years ago, hide # |
 
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Congratulations to neal for taking the first place XD !!!

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2 years ago, hide # |
 
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Why my solution for F was hacked? Just because the time constant?

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2 years ago, hide # |
 
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a trend of not able to solve E and getting hacked on F continues

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2 years ago, hide # |
 
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Took me embarrassingly long and with many false attempts to solve E. Solved F and G before it.

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

    a recent trend is to give a constructive problem as div -3,4 E making it confusing wheather to go for e or f

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2 years ago, hide # |
 
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I have rating less than 1600, but this contest is displaying in unrated section in my profile?

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    2 years ago, hide # ^ |
     
    Vote: I like it +4 Vote: I do not like it

    That is only because the ratings are not currently calculated

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      2 years ago, hide # ^ |
       
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      hi. i am a beginner here. just wanted to ask. now, since the hacking phase is over, by when(approximately) will the rating be shown?

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        2 years ago, hide # ^ |
         
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        After the hacking phase, all solutions will be rerun with the new test cases generated during the hacking phase. This is called System Testing. Your rating will be updated after the System Testing, but not immediately; this might take several hours even after the System Testing is complete.

        I expect the overall process to take about a day. However, note that the time required for rating updates can vary.

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2 years ago, hide # |
 
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When can the textual editorial be posted, since youtube isn't accesible in China :(

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2 years ago, hide # |
 
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My rating didn't change even tho I solved 2 questions?

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2 years ago, hide # |
 
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I hacked four solutions of E using the testcase where t=100 and n from 1 to 100. Now as the system tests are visible the second testcase is same as my hack test. How is this possible ?

Hack test — https://codeforces.me/contest/1992/hacks/1055241/test

Submission Link — https://codeforces.me/contest/1992/submission/270051562

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    2 years ago, hide # ^ |
     
    Vote: I like it +1 Vote: I do not like it

    It's because their solution is barely passing the time limit, so run to run variance. If it was ran again it might pass and it might not

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2 years ago, hide # |
 
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I am unrated and a newbie right now but still this round is showing unrated for me..

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    2 years ago, hide # ^ |
     
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    Dude system testing hasn't started yet. The ratings dont change until its done

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    2 years ago, hide # ^ |
     
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    Since you are a newcomer, this round will be rated for you. It seems you saw your rating graph with the 'All' filter. However, this does not mean that you are unrated for this round; it simply means that the ratings have not been finalized yet.

    Please wait for the system testing to be completed. After the system testing is done, you can expect your rating to be updated.

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2 years ago, hide # |
 
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I had submitted 3 questions in the Codeforces Round 472 (rated, Div. 2, based on VK Cup 2018 Round 2) and it was accepted. But when I checked it just now it is not showing my submitted answers and my first question is highlighted red. Also is showing some system checking which is at 77%. Please tell me what is going on as I am new to Code Forces.

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    2 years ago, hide # ^ |
     
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    Don't worry, system testing is when all the submissions are checked again on larger amount of tests, the problems that you see "rejected" are actually just unchecked yet, you'll see the true result when system testing is finished.

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2 years ago, hide # |
 
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Can anyone explain what is this hack doing?

https://codeforc.es/contest/1992/hacks/1054913

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2 years ago, hide # |
 
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Before the change of statement, I struggled for a long time to understand problem F as I thought about making more "good segment". It's strange, I don't know why I can't get the real meaning. Why no explanation of the problems?

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2 years ago, hide # |
 
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May I know why this contest is not rated though am a trusted participant.

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2 years ago, hide # |
 
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how to see the test case where I Got hacked I cannot see it in hacks section, as well as there is no test case visible to me with wrong answer verdict

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

    Just follow the instructions on the image. Also, during the hacking phase, you cannot see the hacker's input. If you can't view the tests, this might be the reason.

    Here is your test used for hack: Link

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2 years ago, hide # |
 
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Can anyone please help me correct this solution for problem D.

Got WA on 845th test of test case 2.

Code
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    2 years ago, hide # ^ |
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    hey buddy , the problem is the part where you define your state of dp , so what I could understand from the code was dp[i] would give me true/false stating is it possible to go to the end of the river from i.

    There are 2 things that are changing in your recursive function , that is i (index) and k (remaining swimm count) but nowhere in the dp state have you mentioned k there is just i.

    Look at this example lets say when in the first recursive call you get to an index x with remaining swim count as y and it is possible to cross the river with y amount of swimming so dp[x] will be true. but lets say in future you call the same index again with z remaining swim count (z < y) and it is not possible to swim through the river with z swim , still you will be returning "true" because dp[x] is set to true because of first function call.

    Conclusion :

    you need to change the definition of dp[i] , instead of saying dp[i] gives me true or false if it possible to reach end from index i , define dp[i] as minimum number of swimming count required to reach end of river from index i . If it is impossible to reach end from i store some large number which cant be your ans in any case. Keep overflow in mind !!

    AC soln: 270200685

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2 years ago, hide # |
 
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Need Help ,,,, I don't understand how did I get 4 Penalty and -50 on Rating, please can anyone help me for solving this issue, I don't understand I am new here, please anyone there, hello coders

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    2 years ago, hide # ^ |
     
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    +00:04 in the ranking list does not means 4 penalty, it means you take 4 minutes to solve that question.Talking about the rating, you got negative delta bcoz you doesn't perform upto your rating level(before contest rating) in the contest.

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2 years ago, hide # |
 
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I want to be a specialist, any tips for it,as my rating don't seem to change

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2 years ago, hide # |
 
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Where's my rating?

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