//O(NlogN) #include #include #include #include #define int long long using namespace std; using namespace atcoder; int mod = 998244353; int n; vector p; vector fact, finv, inv; //fact[n] = n!, finv[n] = n!の逆元, inv[n] = nの逆元 //参考: よくやる二項係数、https://drken1215.hatenablog.com/entry/2018/06/08/210000 void comb_init(int n) { fact.resize(n); finv.resize(n); inv.resize(n); fact[0] = fact[1] = 1; finv[0] = finv[1] = 1; inv[1] = 1; for (int i = 2; i < n; i++) { fact[i] = fact[i - 1] * i % mod; inv[i] = mod - inv[mod % i] * (mod / i) % mod; finv[i] = finv[i - 1] * inv[i] % mod; } } int comb(int n, int k) { if (n < 0 || k < 0 || n < k) return 0; return fact[n] * finv[k] % mod * finv[n - k] % mod; } signed main() { cin >> n; comb_init(n); p.resize(n); for (int i = 0; i < n; i++) { scanf("%lld", &p[i]); p[i]--; } fenwick_tree fwL(n); vector A(n), B(n); for (int i = 0; i < n; i++) { A[i] = fwL.sum(0, p[i]); B[i] = i - A[i]; fwL.add(p[i], 1); } fenwick_tree fwR(n); vector C(n), D(n); for (int i = n - 1; i >= 0; i--) { C[i] = fwR.sum(0, p[i]); D[i] = n - 1 - i - C[i]; fwR.add(p[i], 1); } int ans = 0; for (int i = 0; i < n; i++) { ans += comb(A[i] + D[i], A[i]) * comb(B[i] + C[i], B[i]) % mod; ans %= mod; } cout << ans << endl; return 0; }