피크닉

#include <iostream>
#include <vector>
#include <string>
using namespace std;

int t, c, n, m;
bool check[45];

void count_pair(int selected, int index, int k, vector<pair<int, int>>& student){
    if(selected == k){
        
        bool student_check[10];
        fill(student_check, student_check+10, false);
        
        for(int i = 0 ; i<m ; i++){
            if(check[i]){
                int a = student[i].first;
                int b = student[i].second;
                if(student_check[a] || student_check[b]) return;
                student_check[a] = true;
                student_check[b] = true;
            }
        }
        c+=1;
        return;
    }
    if(index>=m) return;
    check[index] = true;
    count_pair(selected+1, index+1, k, student);
    check[index] = false;
    count_pair(selected, index+1, k, student);
}

int main() {
    ios_base :: sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    
    cin >> t;
    while(t--){
        vector <pair<int, int>> student;
        c=0;
        cin >> n >> m;
        for(int i = 0 ; i<m ; i++){
            int a, b;
            cin >> a >> b;
            student.push_back(make_pair(a, b));
        }
        count_pair(0, 0, n/2, student);
        cout << c <<'\n';
    }
    return 0;
}

/*
#include <iostream>
#include <string>
using namespace std;
int t, n, m;
bool friends[10][10];


int find_pair(bool taken[10]){
    int ret = 0;
    int first = -1;
    //아직 짝이 없는 친구중 가장 낮은 친구 찾기
    for(int i = 0 ; i<n ; i++){
        if(!taken[i]){
            first = i;
            break;
        }
    }
    
    //모두 짝이 있을 경우
    if(first == -1){
        return 1;
    }
    
    for(int i = first+1 ;  i<n ; i++){
        if(!taken[i] && friends[first][i]){
            taken[first] = taken[i] = true;
            ret += find_pair(taken);
            taken[first] = taken[i] = false;
        }
    }
    return ret;
}

void init(){
    for(int i = 0 ; i<n ; i++)
        for(int j = 0 ; j<n ; j++)
            friends[i][j] = false;
    return;
}

int main() {
    cin >> t;
    
    while(t--){
        cin >> n >> m;
        init();
        for(int i = 0 ; i<m ; i++){
            int a, b;
            cin >> a >> b;
            friends[a][b] = true;
            friends[b][a] = true;
        }
        bool taken[10] ={false, };
        int total_pair = find_pair(taken);
        cout << total_pair << '\n';
    }
    return 0;
}
*/