A. Learning Languages

https://codeforces.com/problemset/problem/277/A

It presents a problem that we need to make all element connected, it can be solved by using dsu.
I didn't use my dsu model and write a simple version of Dsu.

class DSU{
public:
    DSU(int m): size_(m){
        fa_.resize(m);
        std::iota(fa_.begin(), fa_.end(), 0);
    }

    int findSet(int x){
        return fa_[x] == x ? x : fa_[x] = findSet(fa_[x]);
    }

    bool isSameSet(int x, int y){
        return findSet(x) == findSet(y);

    }

    bool unionSet(int u, int v){
        u = findSet(u);
        v = findSet(v);
        if (u == v){
            return false;
        }
        return fa_[u] = v, true;
    }

private:
    vector<int> fa_;
    int size_;
};

void solve(){
    int n, m;
    cin >> n >> m;

    DSU dsu(m + 1);
    vector<int> vis(m + 1);
    int ans = 0;
    for (int i = 0; i < n; ++i){
        int k;
        cin >> k;
        if (!k){
            ans ++;
        }
        int pre = -1;
        while (k --){
            int t;
            cin >> t;
            if (pre != -1){
                dsu.unionSet(pre, t);
            }
            pre = t;
            vis[t] = true;
        }
    }

    for (int i = 1; i <= m; ++i){
        for (int j = i + 1; j <= m; ++j){
            if (vis[i] && vis[j] && dsu.isSameSet(i, j) == false){
                dsu.unionSet(i, j);
                ans ++;
            }
        }
    }

    cout << ans << '\n';
}