220 17661 <558876f0-141f-49ca-bece-7215ec173d1d@isocpp.org> article Path: news.gmane.org!not-for-mail From: Vlad from Moscow Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Overloading the family of minmax algorithms Date: Fri, 1 May 2015 06:47:56 -0700 (PDT) Lines: 206 Approved: news@gmane.org Message-ID: <558876f0-141f-49ca-bece-7215ec173d1d@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1031_1686269933.1430488076203" X-Trace: ger.gmane.org 1430488087 30998 80.91.229.3 (1 May 2015 13:48:07 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 1 May 2015 13:48:07 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCXLLRHD7IDRBDMIR2VAKGQE4CN22SQ@isocpp.org Fri May 01 15:48:06 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ie0-f198.google.com ([209.85.223.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YoBIQ-000463-Nj for gclcip-std-proposals@m.gmane.org; Fri, 01 May 2015 15:48:02 +0200 Original-Received: by iesa3 with SMTP id a3sf167442046ies.0 for ; Fri, 01 May 2015 06:48:01 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:subject:mime-version :content-type:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=aQu6xEa7kMFdG8KXpf+GxQnHNnHq+KeVFQrVn5JfkoE=; b=fWhOd9R+Rn5SmATItQDBSEZ5ZZEj9hKsz2cYwtaSJvOCi4N2cEJWdZtHS0VLANBH6f katrz65PGpbNdrCcFlEC4eJd53zFKAHKzD6R4z9JU4H23oqMxEwuAEpOvOXmdE/cxi06 KNf/SORXo6vcIWyCLYt7lvkTQZrcESCKLaaV7MsKFQ1QOZ6y3cjrM82WOVeUobL9QM2n u40R2awamr0x0GrUCIQGjQF/PwJzJyINfSsCFsJxAJTU3f2c47UPGHoQeg2q/ZqerAke rl90pBLpNpDteLXiFvKj+GbXymb18eiTE7NKd1gKL+vnX/YKiPHnz3Q4BGIi/ZHSjzEk sDOg== X-Gm-Message-State: ALoCoQltnr8lvq4HuV+mFiLNjvHlPGUk7ztJlm9qa5qxN0KmSQtpSvMBn0OLKTK5Bz3bhYgojv0U X-Received: by 10.182.55.105 with SMTP id r9mr17587497obp.3.1430488077692; Fri, 01 May 2015 06:47:57 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.51.77 with SMTP id t71ls1640783qga.10.gmail; Fri, 01 May 2015 06:47:56 -0700 (PDT) X-Received: by 10.140.40.81 with SMTP id w75mr103737qgw.37.1430488076935; Fri, 01 May 2015 06:47:56 -0700 (PDT) X-Original-Sender: vlad.moscow@mail.ru Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:17661 Archived-At: ------=_Part_1031_1686269933.1430488076203 Content-Type: multipart/alternative; boundary="----=_Part_1032_797074472.1430488076203" ------=_Part_1032_797074472.1430488076203 Content-Type: text/plain; charset=UTF-8 As it is known for example standard algorithm std::minmax_element returns a pair of iterators where the first element of the pair points to the first minimum element in the given sequence while the second element of the pair points to the last maximum element in the given sequence. A natural question arises how to apply the algorithm that to find for example the first and last minimum elements or the first and last maximum elements in the given sequence? This task othen occurs in practice. It can be resolved very simple if to introduce an overloaded algorithm that accepts a pair of comparators. It looks the following way template std::pair minmax_element( ForwardIterator first, ForwardIterator last, std::pair comp ); In this case to find for example the first and last minimum elements for the given sequence it is enough to write auto p = ::minmax_element( std::begin( a ), std::end( a ), std::make_pair( std::less<>(), std::greater<>() ) ); Or to find for example the first and last maximum elements for the given sequence it is enough to write auto p = ::minmax_element( std::begin( a ), std::end( a ), std::make_pair( std::greater<>(), std::less<>() ) ); If you will run the following demonstrative program (to write the implementation of the algorithm is your homework :) ) #include #include #include #include template std::pair minmax_element( ForwardIterator first, ForwardIterator last, std::pair comp ) { // ... } int main() { int a[] = { 5, 3, 1, 6, 2, 6, 1 }; auto p = std::minmax_element( std::begin( a ), std::end( a ) ); std::cout << "min: " << std::distance( std::begin( a ), p.first ) << std::endl; std::cout << "max: " << std::distance( std::begin( a ), p.second ) << std::endl; std::cout << std::endl; p = ::minmax_element( std::begin( a ), std::end( a ), std::make_pair( std::less<>(), std::greater<>() ) ); std::cout << "min: " << std::distance( std::begin( a ), p.first ) << std::endl; std::cout << "min: " << std::distance( std::begin( a ), p.second ) << std::endl; std::cout << std::endl; p = ::minmax_element( std::begin( a ), std::end( a ), std::make_pair( std::greater<>(), std::less<>() ) ); std::cout << "max: " << std::distance( std::begin( a ), p.first ) << std::endl; std::cout << "max: " << std::distance( std::begin( a ), p.second ) << std::endl; } you get the following output min: 2 max: 5 min: 2 min: 6 max: 3 max: 5 -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. ------=_Part_1032_797074472.1430488076203 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
As it is known for example standard algorithm std::mi= nmax_element returns a pair of iterators where the first element of the pai= r points to the first minimum element in the given sequence while the secon= d element of the pair points to the last maximum element in the given seque= nce.

A natural question arises how to apply the al= gorithm that to find for example the first and last minimum elements o= r the first and last maximum elements in the given sequence?

=
This task othen occurs in practice.

It can be resolved very simple if to introduce an overloaded a= lgorithm that accepts a pair of comparators.

It lo= oks the following way

template <class ForwardIt= erator, class Compare1, class Compare2>
std::pair<ForwardIterator,= ForwardIterator>
minmax_element( ForwardIterator first,
 &n= bsp;            = ;  ForwardIterator last,
       =          std::pair<Compare1, Com= pare2> comp );

In this case to find for example= the first and last minimum elements for the given sequence it is enough to= write

    auto p =3D ::minmax_elem= ent( std::begin( a ), std::end( a ),
      = ;            &n= bsp;            std:= :make_pair( std::less<>(), std::greater<>() ) );

=
Or to find for example the first and last maximum elements = for the given sequence it is enough to write

  &nbs= p; auto p =3D ::minmax_element( std::begin( a ), std::end( a ),
 &n= bsp;            = ;            &n= bsp;    std::make_pair( std::greater<>(), std::less<= ;>() ) );

If you will run the following de= monstrative program (to write the implementation of the algorithm is your h= omework :) )

#include <iostream>
#include= <algorithm>
#include <iterator>
#include <functional&= gt;

template <class ForwardIterator, class Comp= are1, class Compare2>
std::pair<ForwardIterator, ForwardIterator&g= t;
minmax_element( ForwardIterator first,
    &n= bsp;           ForwardIte= rator last,
          =       std::pair<Compare1, Compare2> comp ){
    // ...
}
   &nbs= p;           
=
int main()
{
    int a[] =3D { 5, 3, 1, 6, 2, 6, = 1 };
   
    auto p =3D std::minmax_el= ement( std::begin( a ), std::end( a ) );
   
 &n= bsp;  std::cout << "min: " << std::distance( std::begin( a= ), p.first ) << std::endl;
    std::cout << = "max: " << std::distance( std::begin( a ), p.second ) << std::e= ndl;
   
    std::cout << std::e= ndl;
   
    p =3D ::minmax_element( s= td::begin( a ), std::end( a ),
       = ;            &n= bsp;      std::make_pair( std::less<>(), std= ::greater<>() ) );
    std::cout << "m= in: " << std::distance( std::begin( a ), p.first ) << std::endl= ;
    std::cout << "min: " << std::distance( = std::begin( a ), p.second ) << std::endl;
   
&= nbsp;   std::cout << std::endl;
   
&= nbsp;   p =3D ::minmax_element( std::begin( a ), std::end( a ),            &= nbsp;           &nbs= p; std::make_pair( std::greater<>(), std::less<>() ) );
    std::cout << "max: " << std::distance( st= d::begin( a ), p.first ) << std::endl;
    std::cou= t << "max: " << std::distance( std::begin( a ), p.second ) <= < std::endl;
   
}

you get the following ou= tput

min: 2
max: 5

<= div>min: 2
min: 6

max: 3
max: = 5



--

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To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+unsubscribe@isocpp.org.
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