CODEWITHSUNDEEP
c++stlset
sccs
sccs

Reputation: 1163

(generally) fastest way to remove set intersections

I have two sets test and test1 and I need to remove elements from test that exist in test1 e.g.

if test contains 1,2,3,4,5 and test1 contains 3,5,6,7: then the function should be performed on test so only 1,2,4 are left in it.

I've discovered set_intersection - is that the best way of doing things?

edit: apologies. both test and test1 are set<int>

Upvotes: 1

Views: 411

Answers (2)

Vijay
Vijay

Reputation: 67221

This should work. I haven't tested it though. You can use :

set_difference(test.begin(), test.end(),test1.begin(),test1.end(),std::inserter(test, test.end()));

Upvotes: 3

mattn
mattn

Reputation: 7723

set doesn't have non-const iterator. use list and remove_if.

#include <iostream>
#include <list>
#include <algorithm>

int
main(int argc, char* argv[]) {
  std::list<int> test = {1,2,3,4,5};
  std::list<int> test1 = {3,5,6,7};

  std::list<int>::iterator ri = std::remove_if(test.begin(), test.end(), [&](int x) -> bool {
    return std::find(test1.begin(), test1.end(), x) != test1.end();
  });
  test.erase(ri, test.end());
  std::for_each(test.begin(), test.end(), [&](decltype(test)::value_type x) {
    std::cout << x << std::endl;
  });
  return 0;
}

Upvotes: 0

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