C++ Tutorial/STL Algorithms Binary search/equal range

equal_range and distance

<source lang="cpp">/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <vector>
3. include <deque>
4. include <list>
5. include <set>
6. include <map>
7. include <string>
8. include <algorithm>
9. include <iterator>
10. include <functional>
11. include <numeric>

using namespace std; /* PRINT_ELEMENTS()

* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/

template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {

   typename T::const_iterator pos;
   std::cout << optcstr;
   for (pos=coll.begin(); pos!=coll.end(); ++pos) {
       std::cout << *pos << " ";
   }
   std::cout << std::endl;

} /* INSERT_ELEMENTS (collection, first, last)

* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/

template <class T> inline void INSERT_ELEMENTS (T& coll, int first, int last) {

   for (int i=first; i<=last; ++i) {
       coll.insert(coll.end(),i);
   }

}

int main() {

   list<int> coll;
   INSERT_ELEMENTS(coll,1,9);
   INSERT_ELEMENTS(coll,1,9);
   coll.sort ();
   PRINT_ELEMENTS(coll);
   // print first and last position 5 could get inserted
   pair<list<int>::iterator,list<int>::iterator> range;
   range = equal_range (coll.begin(), coll.end(),
                        5);
   cout << "5 could get position "
        << distance(coll.begin(),range.first) + 1
        << " up to "
        << distance(coll.begin(),range.second) + 1
        << " without breaking the sorting" << endl;

}</source>

1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9
5 could get position 9 up to 11 without breaking the sorting

equal_range( v.begin(), v.end(), 6 )

<source lang="cpp">#include <iostream>

1. include <algorithm>
2. include <vector>

using namespace std; int main() {

  const int SIZE = 10;
  int a1[] = { 2, 2, 4, 4, 4, 6, 6, 6, 6, 8 };
  vector< int > v( a1, a1 + SIZE );
  pair< vector< int >::iterator, vector< int >::iterator > eq;
  eq = equal_range( v.begin(), v.end(), 6 );
  cout << "\nUsing equal_range:\n" << "   Lower bound of 6 is element "
       << ( eq.first - v.begin() ) << " of vector v";
  cout << "\n   Upper bound of 6 is element "
       << ( eq.second - v.begin() ) << " of vector v";
  return 0;

}</source>

Use equal function to check for corresponding even and odd elements

<source lang="cpp">/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <vector>
3. include <deque>
4. include <list>
5. include <set>
6. include <map>
7. include <string>
8. include <algorithm>
9. include <iterator>
10. include <functional>
11. include <numeric>

/* PRINT_ELEMENTS()

* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/

template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {

   typename T::const_iterator pos;
   std::cout << optcstr;
   for (pos=coll.begin(); pos!=coll.end(); ++pos) {
       std::cout << *pos << " ";
   }
   std::cout << std::endl;

} /* INSERT_ELEMENTS (collection, first, last)

* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/

template <class T> inline void INSERT_ELEMENTS (T& coll, int first, int last) {

   for (int i=first; i<=last; ++i) {
       coll.insert(coll.end(),i);
   }

}

using namespace std; bool bothEvenOrOdd (int elem1, int elem2) {

   return elem1  2;

}

int main() {

   vector<int> coll1;
   list<int> coll2;
   INSERT_ELEMENTS(coll1,1,7);
   INSERT_ELEMENTS(coll2,3,9);
   PRINT_ELEMENTS(coll1,"coll1: ");
   PRINT_ELEMENTS(coll2,"coll2: ");
   // check for corresponding even and odd elements
   if (equal (coll1.begin(), coll1.end(),  // first range
              coll2.begin(),               // second range
              bothEvenOrOdd)) {            // comparison criterion
       cout << "even and odd elements correspond" << endl;
   }
   else {
       cout << "even and odd elements do not correspond" << endl;
   }

}</source>

coll1: 1 2 3 4 5 6 7
coll2: 3 4 5 6 7 8 9
even and odd elements correspond

Use equal function to check whether both collections are equal

<source lang="cpp">/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <vector>
3. include <deque>
4. include <list>
5. include <set>
6. include <map>
7. include <string>
8. include <algorithm>
9. include <iterator>
10. include <functional>
11. include <numeric>

/* PRINT_ELEMENTS()

* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/

template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {

   typename T::const_iterator pos;
   std::cout << optcstr;
   for (pos=coll.begin(); pos!=coll.end(); ++pos) {
       std::cout << *pos << " ";
   }
   std::cout << std::endl;

} /* INSERT_ELEMENTS (collection, first, last)

* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/

template <class T> inline void INSERT_ELEMENTS (T& coll, int first, int last) {

   for (int i=first; i<=last; ++i) {
       coll.insert(coll.end(),i);
   }

}

using namespace std; int main() {

   vector<int> coll1;
   list<int> coll2;
   INSERT_ELEMENTS(coll1,1,7);
   INSERT_ELEMENTS(coll2,3,9);
   PRINT_ELEMENTS(coll1,"coll1: ");
   PRINT_ELEMENTS(coll2,"coll2: ");
   // check whether both collections are equal
   if (equal (coll1.begin(), coll1.end(),  // first range
              coll2.begin())) {            // second range
       cout << "coll1 == coll2" << endl;
   }
   else {
       cout << "coll1 != coll2" << endl;
   }

}</source>

coll1: 1 2 3 4 5 6 7
coll2: 3 4 5 6 7 8 9
coll1 != coll2

Use equal_range to determine both the lower- and upper-bound insertion points

<source lang="cpp">#include <iostream> using std::cout; using std::endl;

1. include <algorithm>
2. include <vector>
3. include <iterator>

int main() {

  int a1[ 10 ] = { 2, 2, 4, 4, 4, 6, 6, 6, 6, 8 };
  std::vector< int > v( a1, a1 + 10 );
  std::ostream_iterator< int > output( cout, " " );
  std::copy( v.begin(), v.end(), output );
  std::pair< std::vector< int >::iterator, std::vector< int >::iterator > eq;
  eq = std::equal_range( v.begin(), v.end(), 6 );
  cout << "\n\n\nLower bound of 6 is element " << ( eq.first - v.begin() ) << " of vector v \n\n\n";
  cout << "Upper bound of 6 is element " << ( eq.second - v.begin() ) << " of vector v";
  return 0;

}</source>

2 2 4 4 4 6 6 6 6 8

Lower bound of 6 is element 5 of vector v

Upper bound of 6 is element 9 of vector v

Use equal_range to locate the first and last point at which 5 can be inserted in order

<source lang="cpp">#include <iostream>

1. include <algorithm>
2. include <vector>

using namespace std; int main() {

  const int SIZE = 10;
  int a1[] = { 2, 2, 4, 4, 4, 6, 6, 6, 6, 8 };
  vector< int > v( a1, a1 + SIZE );
  pair< vector< int >::iterator, vector< int >::iterator > eq;
  cout << "\n\nUse equal_range to locate the first and last point at which 5 can be inserted in order";
  eq = equal_range( v.begin(), v.end(), 5 );
  cout << "\n   Lower bound of 5 is element "
       << ( eq.first - v.begin() ) << " of vector v";
  cout << "\n   Upper bound of 5 is element "
       << ( eq.second - v.begin() ) << " of vector v" 
       << endl;            
  return 0;

}</source>