# Untitled

user_5668965
c_cpp
18 days ago
1.0 kB
1
Indexable
Never
```#include <bits/stdc++.h>

using namespace std;

#define x first
#define y second
#define pb push_back
#define mp make_pair
#define sqr(a) ((a) * (a))
#define sz(a) int((a).size())
#define all(a) (a).begin(), (a).end()
#define forn(i, n) for (int i = 0; i < int(n); ++i)

const int MOD = 998244353;
const int N = 1e6 + 7;

int n;
vector<int> a[N];
int cnt[N];
int inv[N];

int add(int a, int b) {
a += b;
if (a >= MOD) a -= MOD;
return a;
}

int mul(int a, int b) {
return a * 1ll * b % MOD;
}

int binpow(int a, int b) {
int res = 1;
while (b) {
if (b & 1) res = mul(res, a);
a = mul(a, a);
b >>= 1;
}
return res;
}

int main() {
scanf("%d", &n);
forn(i, n) {
int k;
scanf("%d", &k);
a[i].resize(k);
forn(j, k) scanf("%d", &a[i][j]);
forn(j, k) cnt[a[i][j]]++;
}

forn(i, N) inv[i] = binpow(i, MOD - 2);

int ans = 0;
forn(i, n) for (auto x : a[i])
ans = add(ans, mul(mul(inv[n], inv[sz(a[i])]), mul(cnt[x], inv[n])));

printf("%d\n", ans);
}```