Re: comparing elements of vector<int> and list<int>

From:
red floyd <no.spam@here.dude>
Newsgroups:
comp.lang.c++
Date:
Tue, 09 Oct 2007 12:17:16 -0700
Message-ID:
<9tQOi.1158$R95.229@nlpi070.nbdc.sbc.com>
AnonMail2005@gmail.com wrote:

On Oct 9, 12:45 pm, arnuld <geek.arn...@gmail.com> wrote:

It is quite an ugly hack but it is all I am able to come up with for
now :-( and it does the requires work. I want to improve the program, I
know you people have much better ideas ;-)

/* C++ Primer - 4/e
 *
 * exercise 9.20
 * STATEMENT:
 * Write a program to to compare whether a vector<int> contains the
 * same elements as a list<int>.
 *
 */

#include <iostream>
#include <vector>
#include <list>
#include <algorithm>
#include <iterator>

int main()
{
  std::cout << "Enter some integers for VECTOR: ";
  std::vector<int> ivec;
  std::copy( std::istream_iterator<int>( std::cin ),
             std::istream_iterator<int>(),
             std::back_inserter( ivec ) );

  std::cin.clear();
  std::cout << "Enter some integers for LIST: ";
  std::list<int> ilist;
  std::copy( std::istream_iterator<int>( std::cin ),
             std::istream_iterator<int>(),
             std::back_inserter( ilist ) );

  std::cout << "\nNow we will compare VECTOR & LIST for equality :: ";

  bool comp_result = true;
  std::vector<int>::const_iterator viter = ivec.begin();
  std::list<int>::const_iterator liter = ilist.begin();

  /* If sizes are unequal, then they can not be equal :-) */
  if( ivec.size() != ilist.size() )
    {
      comp_result = false;
    }
  else
    {
      for( ; ( viter != ivec.end() ) || ( liter != ilist.end() );
           ++viter, ++liter )
        {
          if( *viter != *liter )
            {
          comp_result = false;
            }
        }
    }

  if( comp_result )
    {
      std::cout << "VECTOR & LIST are EQUAL" << std::endl;
    }
  else
    {
      std::cout << "VECTOR & LIST are NOT equal" << std::endl;
    }

  return 0;

}

========= A FEW RUNS =================
~/programming/c++ $ g++ -ansi -pedantic -Wall -Wextra ex_09-20.cpp
~/programming/c++ $ ./a.out
Enter some integers for VECTOR: 1 2 3
Enter some integers for LIST: 1 2 1

Now we will compare VECTOR & LIST for equality :: VECTOR & LIST are NOT equal
~/programming/c++ $ ./a.out
Enter some integers for VECTOR: 1
Enter some integers for LIST: 1 2 3 4 5 6 7 8 9 0 9 9 8 8 8 8 8 8 8 8 8 8
8 8 8 88 88 88 8 8 8 88 8 8 88 8 8 8 8 8 8 8 8

Now we will compare VECTOR & LIST for equality :: VECTOR & LIST are NOT equal
~/programming/c++ $ ./a.out
Enter some integers for VECTOR: 1 2 3
Enter some integers for LIST: 1 2 3

Now we will compare VECTOR & LIST for equality :: VECTOR & LIST are EQUAL
~/programming/c++ $ ./a.out
Enter some integers for VECTOR: 1 2 3
Enter some integers for LIST: 1 2

Now we will compare VECTOR & LIST for equality :: VECTOR & LIST are NOT
equal

-- arnuldhttp://lispmachine.wordpress.com


You could also try std::equal for containers of the same length.

Also, your code should stop looping as soon as an element doesn't
match.

hth


So, it's easy to say:

if (ivec.size() != ilist.size())
     return false;
else
     return std::equal(ivec.begin(), ivec.end(), ilist.begin());

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