Educational Codeforces Round 79 (Rated for Div. 2) D题

先选一个人，再从这个人中选一个礼物，再随机选一个人，求选的这个礼物恰好是这个人想要的概率

int mod = 998244353;
int p[MAXN];
vector vec[MAXN];

ll powmod(ll a,ll b,ll p) {
    ll res = 1;
    while(b) {
        if(b&1) res = res*a%p;
        a = a*a%p;
        b >>= 1;
    }
    return res;
}

ll getp(ll x, ll y) {
    return x*powmod(y,mod-2,mod)%mod;
}

int main() {
    love;
    int n,k,x;
    cin >> n;
    for(int i = 1; i <= n; i++) {
        cin >> k;
        for(int j= 1; j <= k; j++) {
            cin >> x;
            vec[i].push_back(x);
        }
    }
    ll pone = getp(1,n);
    for(int i = 1; i <= n; i++) {
        int sum = vec[i].size();
        for(int j = 0;j < vec[i].size();j++) {
            p[vec[i][j]] = (p[vec[i][j]] + pone*getp(1,sum)%mod)%mod;
        }
    }
    ll ans = 0;
    for(int i = 1; i <= n; i++) {
        for(int j = 0; j < vec[i].size(); j++) {
            ans = (ans + pone * p[vec[i][j]] % mod) % mod;
        }
    }
    cout << ans << endl;
    system("pause");
    return 0;
}