C++ Tutorial/STL Algorithms Merge/set intersection

Determine elements in both two sets

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

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

int main() {

  const int SIZE1 = 10, SIZE2 = 5, SIZE3 = 20;
  int a1[ SIZE1 ] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
  int a2[ SIZE2 ] = { 4, 5, 6, 7, 8 };
  int a3[ SIZE2 ] = { 4, 5, 6, 11, 15 };
  std::ostream_iterator< int > output( cout, " " );
  std::copy( a1, a1 + SIZE1, output );
  cout << "\n";
  std::copy( a2, a2 + SIZE2, output );
  cout << "\n";
  std::copy( a3, a3 + SIZE2, output );
  int intersection[ SIZE1 ];
  int * ptr = std::set_intersection( a1, a1 + SIZE1, a2, a2 + SIZE2, intersection );
  cout << "nset_intersection of a1 and a2 is: ";
  std::copy( intersection, ptr, output );
     
  return 0;

}</source>

1 2 3 4 5 6 7 8 9 10
4 5 6 7 8
4 5 6 11 15 nset_intersection of a1 and a2 is: 4 5 6 7 8

Illustrate set_intersection

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

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

using namespace std; int main() {

 bool result;
 string s("abcde");
 string s2("aeiou");
 vector<char> vector1(s.begin(), s.end());
 vector<char> vector2(s2.begin(), s2.end());
 
 vector<char> setIntersection;
 set_intersection(vector1.begin(), vector1.end(),vector2.begin(), vector2.end(),back_inserter(setIntersection));
 for(int i=0;i<setIntersection.size();i++){
   cout << setIntersection[i];
 }
 return 0;

}</source>

ae

Intersect the ranges by using set_intersection()

<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() {

   int c1[] = { 1, 2, 2, 4, 6, 7, 7, 9 };
   int num1 = sizeof(c1) / sizeof(int);
   int c2[] = { 2, 2, 2, 3, 6, 6, 8, 9 };
   int num2 = sizeof(c2) / sizeof(int);
   // print source ranges
   cout << "c1:                         " ;
   copy (c1, c1+num1, ostream_iterator<int>(cout," "));
   cout << endl;
   cout << "c2:                         " ;
   copy (c2, c2+num2, ostream_iterator<int>(cout," "));
   cout << "\n" << endl;
   // intersect the ranges by using set_intersection()
   cout << "set_intersection():         ";
   set_intersection (c1, c1+num1, c2, c2+num2, ostream_iterator<int>(cout," ")

);

   cout << endl;

}</source>

c1:                         1 2 2 4 6 7 7 9
c2:                         2 2 2 3 6 6 8 9
set_intersection():         2 2 6 9