Aly's blog

HOW Can i binary search on a set?????
By Aly, history, 16 months ago, In English

set iterator is not like vector iterator i cant add to the iteratire so how can i do binary search on a set and how can i find the diffrence betwen two positions in a set

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16 months ago, # |
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You can use : s.lower_bound(x) s.upper_bound(x)

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    16 months ago, # ^ |
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    thanks , but i want to find the index of the returned iterator from the function

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      16 months ago, # ^ |
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      It's impossible ! :(

      But you can use Ordered_Set

      ref: https://www.geeksforgeeks.org/ordered-set-gnu-c-pbds/

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      16 months ago, # ^ |
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      Sounds like you need a self-balancing binary search tree. You can learn something about __gnu_pbds :: tree, which has implemented one.

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      16 months ago, # ^ |
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      index can be find using distance of required iterator with the begin iterator, distance is present in c++ stl.

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        16 months ago, # ^ |
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        That is O(n) if you use a set (or multiset, for that matter), since iterators work differently in those data structures. The reason it works in O(1) for a vector is that vectors have random-access iterators.

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16 months ago, # |
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You can solve pbds if you are facing problem due to limitations in set and multiset. You can learn it from here: https://www.geeksforgeeks.org/ordered-set-gnu-c-pbds/amp/

Make sure you are using c++20, because pbds use red-black tree and it applies operations in log(n) but it consumes slidely more time than set and multiset.C++20 is faster. So it should be preferred. You can see the blog to realise that: https://mirror.codeforces.com/blog/entry/113537

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16 months ago, # |
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use ordered_set with s.order_of_key(x) which gives the position of x in log(n) time.

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