fcspartakm's blog

By fcspartakm, 3 months ago, translation, In English,
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
 
 
 
 
  • Vote: I like it  
  • +22
  • Vote: I do not like it  

»
3 months ago, # |
  Vote: I like it +1 Vote: I do not like it
»
3 months ago, # |
  Vote: I like it +5 Vote: I do not like it

Very fast! Thank you

»
3 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Thanks for quick explanation. Is there any solution which works faster than "brute solution" for problem D?

  • »
    »
    3 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Faster than O(n)? I think, no.

    • »
      »
      »
      3 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      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?

      • »
        »
        »
        »
        3 months ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        even 5 ways: a1-a2, a1-a2(+-)1,a1-a2(+-)2

      • »
        »
        »
        »
        3 months ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        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

»
3 months ago, # |
  Vote: I like it 0 Vote: I do not like it

For G you don't need to iterate all the exams every day.

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

»
3 months ago, # |
Rev. 2   Vote: I like it +4 Vote: I do not like it

A simple way of understanding 978E - Bus Video System:

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.

»
3 months ago, # |
  Vote: I like it +2 Vote: I do not like it

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.

»
3 months ago, # |
  Vote: I like it 0 Vote: I do not like it

My solution 38178463 to problem 978E - Bus Video System is O(n).

»
3 months ago, # |
  Vote: I like it +3 Vote: I do not like it

My solution 38166452 to problem 978B - File Name was similar to the one in the tutorial, but easiest, it's how many ocurrences have the string "xxx" in the string s.

»
3 months ago, # |
  Vote: I like it 0 Vote: I do not like it

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".

»
3 months ago, # |
  Vote: I like it 0 Vote: I do not like it

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())))
»
3 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Problem E can be solvable using binary search on answer . :) . 2 times binary search , first for negative upper bound , second for exceeding lower bound .

»
3 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Other "different" solution for the problem F is using BIT compressed

»
3 months ago, # |
  Vote: I like it 0 Vote: I do not like it

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