[Tutor] Getting greatest 3 numbers from list

[Peter Otten]

On 21/02/2022 14:46, Manprit Singh wrote:
> Dear Sir ,
> 
> This is not related to python, but a general question, in c++ we have sets
> in standard template library and iterators, and sets are basically sorted,
> So doing the same problem in c++ using sets is a bad idea ?
> 
> #include<iostream>
> #include<set>
> #include<functional>
> using namespace std;
> 
> int main()
> {
>      int arry[6] = {2, 4, 9, 2, 4, 1};
>      set<int> second(arry, arry+6);
>      auto itr = second.end();
>      itr--;
>      auto greatest = *itr;
>      itr--;
>      auto seclargest = *itr;
>      itr--;
>      auto thirdlargest = *itr;
>      cout << greatest << " " << seclargest << " "<<thirdlargest;
>      return 0;
> }
> 
> Gives the right answer
> 
> My apologies for posting c++ code if it is against the rule of python
> mailing list

Well, don't make it a habit ;)

I suppose the above is roughly equivalent to

 >>> sorted(set([2, 4, 9, 2, 4, 1]))[-3:]
[2, 4, 9]

This produces different results when the list contains duplicates:

 >>> items = [1, 2, 3, 3, 2, 1]
 >>> sorted(set(items))[-3:]
[1, 2, 3]
 >>> sorted(items)[-3:]
[2, 3, 3]

Also, can the C++ code cope with input consisting of less than three 
different values?

Finally, when you pick a complex tool like C++ you usually want 
something algorithmically efficient -- which reminds me of the heap I 
mentioned above...