fcspartakm's blog

By fcspartakm, 2 years ago, translation, In English
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Tutorial of Pactice
Tutorial of W9 novice contest
 
 
 
 
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2 years ago, # |
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2 years ago, # |
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Very fast! Thank you

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2 years ago, # |
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Thanks for quick explanation. Is there any solution which works faster than "brute solution" for problem D?

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    2 years ago, # ^ |
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    Faster than O(n)? I think, no.

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      2 years ago, # ^ |
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      We need to iterate over massive in cases of changing first and second elements. So as our first element could be changed in 3 ways and second element could be changed in 3 ways we have O(n*m) where m = number of combinations of first and second element changes (in our case 3*3). Maybe my question was not clearly. Is there any way to generalize algorithm to work not only with changes between [-1, 1] but also with general case [-i, i] not in O(n*m) complexity?

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        2 years ago, # ^ |
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        even 5 ways: a1-a2, a1-a2(+-)1,a1-a2(+-)2

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        2 years ago, # ^ |
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        Hello! I've solved it by calculating an average value of the common difference. But there are tricky cases when n equals 4 or 5. 38261362

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2 years ago, # |
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For G you don't need to iterate all the exams every day.

38195700 complexity is O(n*logm) insted of O(n*m)

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2 years ago, # |
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A simple way of understanding 978E - Система видеонаблюдения в автобусе:

Define pre[i]  = 

Let's take an arbitrary variable initial which could hold all possible initial values.

It is easy to see this inequality holds true:

0  ≤  initial + pre[i]  ≤  w,

Which implies:

 - pre[i]  ≤  initial  ≤  w - pre[i]

We can reduce this to:

max(0,  - pre[i])  ≤  initial  ≤  min(w, w - pre[i])

Solving this inequality and finding the range gives us the final answer.

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2 years ago, # |
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For F instead of using vectors with quarrels another nice way is to process the quarrels by incrementing an array containing the "number of quarrels with less skilled programmers". Then we can just directly subtract the number in that array at the end.

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2 years ago, # |
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My solution 38166452 to problem 978B - Имя файла was similar to the one in the tutorial, but easiest, it's how many ocurrences have the string "xxx" in the string s.

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2 years ago, # |
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fcspartakm I think there was a typo in the tutorial of problem F: "we can user array of pairs" for "we can use array of pairs".

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2 years ago, # |
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Regexp solution is very easy to write for B :P

print sum(map(lambda x : len(x) - 3 + 1, re.findall('x{3,}', raw_input())))
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2 years ago, # |
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Problem E can be solvable using binary search on answer . :) . 2 times binary search , first for negative upper bound , second for exceeding lower bound .

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2 years ago, # |
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Other "different" solution for the problem F is using BIT compressed

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2 years ago, # |
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In problem 978D: "Almost Arithmetic Progression" I'm failing in test case 17. 3 34 70 52 But this is already an AP. The answer should be 0. But the jury's answer for this is -1. Please help where I am mistaken.

My solution: https://codeforces.com/contest/978/submission/38594533