deepak_097's blog

SPOJ [ QTREE — Query on a tree ] problem.
By deepak_097, history, 8 years ago, In English

Please help me to optimise my code i am getting TLE since 6 hours.

problem link- link solution link- link

I tried every possible way to get rid over TLE but nothing works.

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8 years ago, hide # |
 
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I too got suck on this one when I first tried it due to strict TL.

Btw, just don't use anything for max (like function, macro or stl) just write if() else (), and you will be fine(probably).

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8 years ago, hide # |
 
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I didn't read your code but when the tree is a line, HLD maybe get TLE

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    8 years ago, hide # ^ |
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    Uhm.. I'm sorry, what? HLD on a line tree is just a segment tree. The complexity of query on that tree is . On random trees HLD query complexity is about

    What about TLE on problem. Did you try to debug some edge cases? It seems like your solution is not working when n = 1

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    8 years ago, hide # ^ |
     
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    HLD assures O(log^2 n) per query (in this problem).

    Especially when tree is a line,( there is only one chain) that is same as querying on sequence. Which is O(log n).

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8 years ago, hide # |
 
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I solved it in another online judge, using HLD. I guess there might be mistake in your code but i couldn't find it.. sorry

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    8 years ago, hide # ^ |
     
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    Yes i found out the mistake but unable to understand why it's happening :(

    My Accepted Soln- link in 0.33sec

    I just changed the behaviour of my ancestor 2-d array from anc[i][j] to anc[j][i] and it got accepted but the problem is even in both cases it has samecomplexity of O(15*sz) but anc[i][j] is giving TLE and anc[j][i] is giving the answer within time limit.

    Please help me to find out the mistake that i was doing.

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      8 years ago, hide # ^ |
       
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      Well, IMO, this is just cache localisation. While finding the ancestors, in case of lca we are using anc[j][i] and then immediately anc[j][i+1] which helps cache localisation.

      On the other hand, if you are using anc[i][j] and then anc[i+1][j] there is a gap of around 15 between these and it is unable to use the cache efficiently.

      Generally this doesn't matter much but this question seems to have a very strict TL.

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