vovuh's blog

By vovuh, history, 4 years ago, In English

1003A - Polycarp's Pockets

Tutorial
Solution (Vovuh)

1003B - Binary String Constructing

Tutorial
Solution (Vovuh)

1003C - Intense Heat

Tutorial
Solution (PikMike)

1003D - Coins and Queries

Tutorial
Solution (Vovuh)

1003E - Tree Constructing

Tutorial
Solution (Vovuh)

1003F - Abbreviation

Tutorial
Solution (Vovuh)
 
 
 
 
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4 years ago, # |
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In E, won't the distance change upon inserting new edges and if yes, how to update the "maximal distance set" efficiently?

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    4 years ago, # ^ |
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    The previous explanation was wrong, i had understood it now.

    If the distance for some vertex v will change after adding the new vertex, it means that we attach some leaf that increases the diameter of a tree. But it means that we attach a leaf to the vertex w with distw = d, but in this case we already doesn't have the answer.

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    4 years ago, # ^ |
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    It is possible to prove that there exists such a tree iff n * (k - 2) <= -2 + k * (k - 1) ** (d // 2) for even n and n * (k - 2) <= -2 + k * (k - 1) ** (d // 2) + (k - 2) * (k - 1) ** (d // 2)for odd n. We simply check if conditions above are satisfied and proceed with making the tree or not.

    Edit: also, obviously it must be that n > d as said in the article

    Edit: k = 1 and k = 2 should be treated as special cases

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4 years ago, # |
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:

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4 years ago, # |
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My solution to F was to assign an integer to each distinct string (since there's a maximum of 300) while keeping track of lengths for each of these integers and then run a KMP search to find the number of occurrences of each valid subsequence. This solution runs in approximately the same time complexity as the editorial's.

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4 years ago, # |
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There is an O(n) approach in problem C.

code

rough explanation

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    4 years ago, # ^ |
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    your pish and pop operations aren't constant time operations.

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      4 years ago, # ^ |
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      But each node would be push and pop 1 time.

      I don't know why so much downvotes.

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        4 years ago, # ^ |
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        No idea why you're getting downvotes (that shouldn't matter tho, if you think your comment is constructive), your solution is very efficient.

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          4 years ago, # ^ |
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          It is a classic method to optimize DP.

          I think I am doing nothing wrong to point it out in the case that editorial doesn't mention.

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    4 years ago, # ^ |
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    It seems that people are likely to downvote algorithm they don't know.

    I think that is a very simple way to analysis the complexity, but it might be far too difficult for those rating is under 1600?

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    4 years ago, # ^ |
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    Can you please explain your solution?

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4 years ago, # |
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what wrong in problem F makes a lotta participants output 689 in test 6 instead of 581?

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    4 years ago, # ^ |
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    Those solutions most likely did not consider more than two segments (only exactly two). The sample tests did not cover this.

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4 years ago, # |
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what is wrong with my solution for D:https://codeforces.com/contest/1003/submission/39974183

or mby i am not getting editorial??

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4 years ago, # |
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can anyone explain me the method for Problem C becoz despite several efforts i m unable to figure it out

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    4 years ago, # ^ |
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    my approach is quite simple what I have done is to check for all segments the average temperature and we will consider which gives best answer and has size >= k my code

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      4 years ago, # ^ |
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      Bro really thanks for ur help my approach is also quite the same but i got a TLE i m giving my code link plz help as I m beginner and really want to increase my skills http://codeforces.com/contest/1003/submission/39983625

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        4 years ago, # ^ |
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        I think "accumulate" as a third for loop .So the complexity is 5e3*5e3*5e3 , it will give you TLE. In worst case if n is 5e3 and k is 1 .

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          4 years ago, # ^ |
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          thanx bro ,,,, rest i think my algorithm is correct am I right??

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            4 years ago, # ^ |
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            You're right,but in this problem you don't have to use "accumulate".Think in a different way.

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              4 years ago, # ^ |
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              i fixed by using sum=sum+v[i];

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                4 years ago, # ^ |
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                Try it : ) . If it gives you a wrong answer , think about "what is the wrong in your code and what is the test you will fail in ", if you don't know , tell me , I will help you : ) .

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                  4 years ago, # ^ |
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                  thanx bro ...i passed all the test cases... thanx for ur help

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4 years ago, # |
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In problem D my code passed all pretests but it timed out on 27th Case in system testing. No wonder how. Code complexity Q * 32 * 32. Can someone suggest something? Code

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    4 years ago, # ^ |
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    unordered_map operations works some more than O(1).

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    4 years ago, # ^ |
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    U can easily adjust to only Q * 32 operations with a greedy strategy. A complexity has no constants is it. your complexity is O(Q) if you say so. Map operations are O(log) so the number of operations is even worse in your solution. Just adapt to O(Q * log(MAX_VALUE) + N * log(MAX_VALUE)) which actually is O(N * log(VAX_VALUE)) because N and Q constrains are the same. Now to adapt you can just do this:

    the solution
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4 years ago, # |
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Could someone explain why it didn't pass even the pretests? (problem D, WA test 4)

Code

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4 years ago, # |
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What do think is wrong with my sol for binary string problem here: http://codeforces.com/contest/1003/submission/39907389 I believe it runs perfectly on the four cases you mentioned in your blog

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4 years ago, # |
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For Question B: Binary String Constructing, is there a recursive approach? Does anyone know similar problems like this, where it has a large number of generalized test cases?

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4 years ago, # |
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4 years ago, # |
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why it times out on test 23?? (problem E) http://codeforces.com/contest/1003/submission/39989027 but if i assign the values of test 23 and upload the code here it will not time out!!: http://codeforces.com/contest/959/submission/39989086 why????????????? :(

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4 years ago, # |
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anyone with better explanation of F using DP

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4 years ago, # |
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Is it possible to solve problem D using Python?

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4 years ago, # |
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can anyone tell me what does __builtin_ctz(x) do?

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4 years ago, # |
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Why is a random_shuffle performed at the end of the code for problem E?

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3 years ago, # |
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Any O(nlogn) or O(n) method for C?

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22 months ago, # |
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I am facing some problem on C problem- Intense Heat. i haven't found any fault in my code but i am stuck in test case 8.

my precision is not matching with judge ans. here is my code my code please help me for this problem. I try to solve it many way but no result. thank you.

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    21 month(s) ago, # ^ |
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    you are checking the maximum heat for segment whose length is exactly k ,but in question you have to check for all segment of length from k to n.

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19 months ago, # |
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what is wrong in my code for C ,it's giving the wrong answer on test#4 https://codeforces.com/contest/1003/submission/85153194

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15 months ago, # |
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For problem E

My proof that when you attach a new node , d(x) of other nodes won't change.

Let d(x) be the distance of the furthest node from x, now when you attach a new node to node u, and say d(w) changes, then u is the furthest node from w (i.e. d(w) = dist(w,u)), so it means u is the end point of the diameter (d(u) = D, because that's the algorithm we use to find the diameter of a tree, finding the furthest node from a random node), so at that point we simple exit the process.

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10 months ago, # |
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I think bool eq[N][N]; is not required since each eq[i][j] cell would be called only once. It is not different from directly comparing s[i] and s[j] in the DP part.