顺丰第一题：

int main() {
    int n, m, k;
    cin >> n >> m >> k;
    vector<vector<int>> peo(n + 1);
    vector<vector<int>> lan(m + 1);
    for (int i = 0; i < k; i++) {
        int a, b;
        cin >> a >> b;
        peo[a].push_back(b);
        lan[b].push_back(a);
    }
    vector<bool> flag(n + 1, false);
    int res = 0;
    for (int i = 1; i <= n; i++) {
        if (flag[i] == false) {
            res++;
            queue<int> q;
            q.push(i);
            flag[i] = true;
            while (!q.empty()) {
                int cur = q.front();
                q.pop();
                for (int i = 0; i < peo[cur].size(); i++) {
                    for (int j = 0; j < lan[peo[cur][i]].size(); j++) {
                        if (flag[lan[peo[cur][i]][j]] == false) {
                            q.push(lan[peo[cur][i]][j]);
                            flag[lan[peo[cur][i]][j]] = true;
                        }
                    }
                }
            }
        }
    }
    if (k == 0)
        cout << res << endl;
    else
        cout << res - 1 << endl;
    system("pause");
    return 0;
}