#include #ifdef LOCAL #include "./debug.cpp" #else #define debug(...) #define print_line #endif using namespace std; using ll = long long; #include /** * @brief Modint */ template struct modint { long long value; modint(long long x = 0) { if (x >= 0) { value = x % MOD; } else { value = MOD - (-x) % MOD; } } modint operator-() const { return modint(-value); } modint operator+() const { return modint(*this); } modint &operator+=(const modint &other) { value += other.value; if (value >= MOD) { value -= MOD; } return *this; } modint &operator-=(const modint &other) { value += MOD - other.value; if (value >= MOD) { value -= MOD; } return *this; } modint &operator*=(const modint other) { value = value * other.value % MOD; return *this; } modint &operator/=(modint other) { (*this) *= other.inv(); return *this; } modint operator+(const modint &other) const { return modint(*this) += other; } modint operator-(const modint &other) const { return modint(*this) -= other; } modint operator*(const modint &other) const { return modint(*this) *= other; } modint operator/(const modint &other) const { return modint(*this) /= other; } modint pow(long long x) const { modint ret(1), mul(value); while (x > 0) { if (x % 2 == 1) { ret *= mul; } mul *= mul; x /= 2; } return ret; } modint inv() const { return pow(MOD - 2); } bool operator==(const modint &other) const { return value == other.value; } bool operator!=(const modint &other) const { return value != other.value; } friend std::ostream &operator<<(std::ostream &os, const modint &x) { return os << x.value; } friend std::istream &operator>>(std::istream &is, modint &x) { long long v; is >> v; x = modint(v); return is; } }; using mod998 = modint<998244353>; using mod107 = modint<1000000007>; using mint = mod998; #include #include /** * @brief Fenwick Tree * @docs docs/data_structure/fenwick_tree.md */ template struct fenwick_tree { fenwick_tree(int n) { this->n = n; dat.resize(n); } void add(int i, T x) { i++; while (i <= n) { dat[i - 1] += x; i += i & -i; } } T operator[](int i) { return sum(i, i + 1); } T sum(int l, int r) { return sum(r) - sum(l); } friend std::ostream &operator<<(ostream &os, fenwick_tree A) { int n = A.n; os << "[ "; for (int i = 0; i < n; i++) { os << A[i]; if (i != n - 1) { os << ", "; } } os << " ]"; return os; } private: int n; std::vector dat; T sum(int r) { T ret = 0; while (r > 0) { ret += dat[r - 1]; r -= r & -r; } return ret; } }; #include /** * @brief Combination */ template struct combination { std::vector fact, factinv; combination(int n) { fact.resize(n + 1); factinv.resize(n + 1); fact[0] = 1; for (int i = 1; i <= n; i++) { fact[i] = fact[i - 1] * i; } for (int i = 0; i <= n; i++) { factinv[i] = fact[i].inv(); } } T nCr(long long n, long long r) { if (n < 0 || r < 0 || n - r < 0) { return 0; } return fact[n] * factinv[r] * factinv[n - r]; } T nPr(long long n, long long r) { if (n < 0 || r < 0 || n - r < 0) { return 0; } return fact[n] * factinv[n - r]; } }; int main() { int N; cin >> N; vector P(N); for (int i = 0; i < N; i++) cin >> P[i], P[i]--; combination C(N); fenwick_tree FT(N); mint ans = 0; for (int i = 0; i < N; i++) { int ls = FT.sum(0, P[i]); int lb = FT.sum(P[i] + 1, N); int rs = P[i] - ls; int rb = N - i - 1 - rs; ans += C.nCr(rb + ls, ls) * C.nCr(lb + rs, rs); FT.add(P[i], 1); } cout << ans << endl; }