meet-in-the-middle

/// https://www.infoarena.ro/blog/meet-in-the-middle
/// ptr SET http://www.cplusplus.com/reference/set/set/
#include <iostream>
#include <set>
using namespace std;
set <int> S,S1,S2;

int main()
{
    int b,sum;
    cin>>b>>sum;
    for(int p1=1;p1<=b;++p1)
        for(int p2=1;p2<=b;++p2)
            S.insert(p1+p2),S1.insert(p1),S2.insert(p2);
    std::pair<std::set<int>::const_iterator,std::set<int>::const_iterator> ret1,ret2;
    for(int p3=1;p3<b;++p3)
        for(int p4=1;p4<b;++p4)
            if(sum-(p3+p4)<=*S.rbegin())
            {
                ret1=S1.equal_range(p3);
                ret2=S2.equal_range(p4);
                cout<<*ret1.first<<' '<<*ret2.first<<' '<<p3<<' '<<p4<<endl;
            }
    return 0;
}

/*
def 4sum(A):
  sums = {}
  for a in A:
    for b in A:
      sums[a + b] = (a, b)

  for c in A:
    for d in A:
      if -(c + d) in sums:
        print (sums[-(c + d)][0], sums[-(c + d)][1], c, d)
        return

  print "No solution."
*/