Backpack with recursion, C++ (gcc)

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//Title of this code
//g++  4.8.2

#include <iostream>
#include <vector>
#include <set>

struct pair {
    int size;
    int value;
    
    pair(int s, int v): size(s), value(v) {}
};

struct retType {
    std::vector<int> arr;
    int best;
};

retType maxPack(std::vector<pair> t, int backSize, std::set<int> usedPos = {}) {
    
    int best = 0;
    int pos = -1;
    std::vector<int> array;
    
    retType retVal;
    
    for (int i = 0; i < t.size(); ++i) {
        
        int size = t[i].size;
        int value = t[i].value;
              
        if (usedPos.find(i) == usedPos.end() && backSize - size >= 0) {

std::set<int> tmpUsedPos = usedPos;
            tmpUsedPos.insert(i);
            
            retType ret = maxPack(t, backSize - size, tmpUsedPos);
            
            if (ret.best + value > best) {
                best = ret.best + value;
                array = ret.arr;
                pos = i;
            }
        }  
    }
    
    if (pos > -1)
        array.push_back(pos);
    
    retVal.arr = array;
    retVal.best = best;
    
    return retVal;
}

int main()
{
    std::vector<pair> stuff = {pair(2,3), pair(1,4), pair(2,5), pair(4,6), pair(3,3)};
    int packSize = 5;
    
    retType rv = maxPack(stuff, packSize);
    
    std::cout << rv.best << std::endl;
    
    
    for (int i = 0; i < rv.arr.size(); ++i)
        
        std::cout << rv.arr[i] << " ";
        
    
}

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Compilation time: 0.62 sec, absolute running time: 0.14 sec, cpu time: 0 sec, memory peak: 3 Mb, absolute service time: 0.77 sec