Set algorithms

Set algorithms include

• includes()
• set_union()
• set_intersection()
• set_difference()
• set_symmetric_difference()

The following, while demonstrating some of these routines, uses 2 ideas that are often useful

• an output stream can be thought of as a container, so you can ``copy'' other containers onto it. The line

  copy(s1.begin(), s1.end(), ostream_iterator<int>(cout," "));
  

  also puts spaces between the integers being printed. For now, don't worry if you don't understand the mechanics - it's useful so just use it!

• Sometimes you won't know how many resulting elements will be produced by an operation, you just want them all added to a container. inserter (which calls the container's insert() routine), front_inserter (which calls the container's push_front() routine - which vectors for example don't have) or back_inserter (which calls push_back()) do that for you.

[fontsize=\small,frame=single,formatcom=\color{progcolor}]
 #include <algorithm>
 #include <set>
 #include <iostream>
 #include <iterator> // needed for ostream_iterator
 using namespace std;

 int main()
 {
   //Initialize some sets
   int a1[10] = {1,2,3,4,5,6,7,8,9,10};
   int a2[6]  = {2,4,6,8,10,12};

   set<int> s1(a1, a1+10), s2(a2, a2+6), answer ;
   cout << "s1=";
   copy(s1.begin(), s1.end(),
        ostream_iterator<int>(cout," "));
   cout << "\ns2=";
   copy(s2.begin(), s2.end(),
        ostream_iterator<int>(cout," "));

   //Demonstrate set_difference
   set_difference(s1.begin(), s1.end(),
                  s2.begin(), s2.end(), inserter(answer,answer.begin()));
   cout << "\nThe set-difference of s1 and s2 =";
   copy(answer.begin(), answer.end(),
        ostream_iterator<int>(cout," "));
   cout << endl;
   return 0;
 }