(C++) std::set_difference

 

std::set_difference is an STL algorithm to create the subset of two sets of which the elements are all present in the first and absent in the second set (stored in any type of container).

 

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#include <algorithm> #include <cassert> #include <iostream> #include <iterator> #include <vector> int main() {   //v contains all values from zero to ten   std::vector<int> v;   v.push_back(0);   v.push_back(1);   v.push_back(2);   v.push_back(3);   v.push_back(4);   v.push_back(5);   v.push_back(6);   v.push_back(7);   v.push_back(8);   v.push_back(9);   //w contains all squares from 1 to an including 25   std::vector<int> w;   w.push_back( 1);   w.push_back( 4);   w.push_back( 9);   w.push_back(16);   w.push_back(25);   //x is the difference of v and w:   //that is, the elements in v, that are   //not in w   std::vector<int> x;   std::set_difference(v.begin(),v.end(),w.begin(),w.end(),     std::back_inserter(x));   //so x contains all three squares between zero to ten   assert(x.size() == 7);   assert(x[0] == 0);   assert(x[1] == 2);   assert(x[2] == 3);   assert(x[3] == 5);   assert(x[4] == 6);   assert(x[5] == 7);   assert(x[6] == 8);   //Show x on screen   std::copy(x.begin(),x.end(),std::ostream_iterator<int>(std::cout," "));   std::cout << '\n'; }