ABC118B - Foods Loved by Everyone

問題：B - Foods Loved by Everyone

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

#define REP(i, n) for (int i = 0; i < (n); ++i)

int main(void) {
    int n, m, k, a, ans = 0;

    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> n >> m;
    vector<int> cnt(m, 0);
    REP(i, n) {
        cin >> k;
        REP(j, k) {
            cin >> a;
            cnt[a - 1]++;
        }
    }

    REP(i, m) {
        if (cnt[i] == n) {
            ans++;
        }
    }

    cout << ans << "\n";
    return 0;
}