How can I iterate through every possible combination of n playing cards

Question

How can I loop through all combinations of n playing cards in a standard deck of 52 cards?

Answer 1

#include 
#include 
using namespace std;

class CombinationsIndexArray {
    vector index_array;
    int last_index;
    public:
    CombinationsIndexArray(int number_of_things_to_choose_from, int number_of_things_to_choose_in_one_combination) {
        last_index = number_of_things_to_choose_from - 1;
        for (int i = 0; i < number_of_things_to_choose_in_one_combination; i++) {
            index_array.push_back(i);
        }
    }
    int operator[](int i) {
        return index_array[i];
    }
    int size() {
        return index_array.size();
    }
    bool advance() {

        int i = index_array.size() - 1;
        if (index_array[i] < last_index) {
            index_array[i]++;
            return true;
        } else {
            while (i > 0 && index_array[i-1] == index_array[i]-1) {
                i--;
            }
            if (i == 0) {
                return false;
            } else {
                index_array[i-1]++;
                while (i < index_array.size()) {
                    index_array[i] = index_array[i-1]+1;
                    i++;
                }
                return true;
            }
        }
    }
};

int main() {

    vector a;
    a.push_back(1);
    a.push_back(2);
    a.push_back(3);
    a.push_back(4);
    a.push_back(5);
    int k = 3;
    CombinationsIndexArray combos(a.size(), k);
    do  {
        for (int i = 0; i < combos.size(); i++) {
            cout << a[combos[i]] << " ";
        }
        cout << "\n";
    } while (combos.advance());

    return 0;
}

Output:

1 2 3 
1 2 4 
1 2 5 
1 3 4 
1 3 5 
1 4 5 
2 3 4 
2 3 5 
2 4 5 
3 4 5