Arpa's blog

By Arpa, history, 2 years ago, In English,

Hello again, It’s Arpa as usual :P. Hope you enjoyed from the Gym, and it’s here is the editorial.

Problem packages are available here. Solutions are available here separately.

Preparation details:

The problems authored by me when the main contest was authoring. Here is a table, showing the percentage of expected accepts (in my opinion, before the contest) and the number of accepts.

A BCD
Expected 100% 30%70%10%
Accepted 27 080

Difference from main problems

A : n is bigger, binary_pow will not work. You need to calculate in a faster way.

B : n and also numbers are much bigger, simple xor will not work.

C : n is bigger, simple LCM will not work because the answer would become really large.

D : Number of alphabets are 26 instead of 22, so it isn’t possible to allocate an array with size 2z (z = 26).

Hints

A : Write the last digit of 1378n for several small values. Calculate in a fast way.

B : Note that if then . Use trie.

C : If the answer exists, it depends on the lengths of cycles in the functional graph. Factorize numbers and calculate LCM.

D : Keep a mask for each vertex, i-th bit of maskv is true if the number of edges in the path from the root to v such that letter i is written on them is odd. Now if number of bits in is 0 or 1, path between v and u is Dokhtar-kosh. Give an id to each mask.

Details

First accepts: A : retired_coder, C : wrinx.

Funniest code : hrzuser ’s code : 23229169. He was managing to get accepted in problem C, with a solution :O.

Solutions

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I’d like to finish the editorial with the below poem by Saadi Shirazi:


مقدار یار همنفس چون من نداند هیچ کس ماهی که بر خشک اوفتد قیمت بداند آب را

Translation: No one knows the value of good friend as I know, fish will know the value of water when it falls on the beach.

Goodbye ; )

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

Actually there was not defference between easy A and hard A because everyone solved them by the same way

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

    Well the base concept is the exact same but calculating the mod is different.

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

What is the difference between this D and it's easier version?

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

    Read the Difference from main problems section.