#pragma GCC optimize("O2") #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include //#define int ll #define INT128_MAX (__int128)(((unsigned __int128) 1 << ((sizeof(__int128) * __CHAR_BIT__) - 1)) - 1) #define INT128_MIN (-INT128_MAX - 1) #define clock chrono::steady_clock::now().time_since_epoch().count() #ifdef DEBUG #define dbg(x) cout << (#x) << " = " << x << '\n' #else #define dbg(x) #endif namespace R = std::ranges; namespace V = std::views; using namespace std; using ll = long long; using ull = unsigned long long; using ldb = long double; using pii = pair; using pll = pair; //#define double ldb template ostream& operator<<(ostream& os, const pair pr) { return os << pr.first << ' ' << pr.second; } template ostream& operator<<(ostream& os, const array &arr) { for(const T &X : arr) os << X << ' '; return os; } template ostream& operator<<(ostream& os, const vector &vec) { for(const T &X : vec) os << X << ' '; return os; } template ostream& operator<<(ostream& os, const set &s) { for(const T &x : s) os << x << ' '; return os; } //reference: https://github.com/NyaanNyaan/library/blob/master/modint/montgomery-modint.hpp#L10 //note: mod should be a prime less than 2^30. template struct MontgomeryModInt { using mint = MontgomeryModInt; using i32 = int32_t; using u32 = uint32_t; using u64 = uint64_t; static constexpr u32 get_r() { u32 res = 1, base = mod; for(i32 i = 0; i < 31; i++) res *= base, base *= base; return -res; } static constexpr u32 get_mod() { return mod; } static constexpr u32 n2 = -u64(mod) % mod; //2^64 % mod static constexpr u32 r = get_r(); //-P^{-1} % 2^32 u32 a; static u32 reduce(const u64 &b) { return (b + u64(u32(b) * r) * mod) >> 32; } static u32 transform(const u64 &b) { return reduce(u64(b) * n2); } MontgomeryModInt() : a(0) {} MontgomeryModInt(const int64_t &b) : a(transform(b % mod + mod)) {} mint pow(u64 k) const { mint res(1), base(*this); while(k) { if (k & 1) res *= base; base *= base, k >>= 1; } return res; } mint inverse() const { return (*this).pow(mod - 2); } u32 get() const { u32 res = reduce(a); return res >= mod ? res - mod : res; } mint& operator+=(const mint &b) { if (i32(a += b.a - 2 * mod) < 0) a += 2 * mod; return *this; } mint& operator-=(const mint &b) { if (i32(a -= b.a) < 0) a += 2 * mod; return *this; } mint& operator*=(const mint &b) { a = reduce(u64(a) * b.a); return *this; } mint& operator/=(const mint &b) { a = reduce(u64(a) * b.inverse().a); return *this; } mint operator-() { return mint() - mint(*this); } bool operator==(mint b) const { return (a >= mod ? a - mod : a) == (b.a >= mod ? b.a - mod : b.a); } bool operator!=(mint b) const { return (a >= mod ? a - mod : a) != (b.a >= mod ? b.a - mod : b.a); } friend mint operator+(mint a, mint b) { return a += b; } friend mint operator-(mint a, mint b) { return a -= b; } friend mint operator*(mint a, mint b) { return a *= b; } friend mint operator/(mint a, mint b) { return a /= b; } friend ostream& operator<<(ostream& os, const mint& b) { return os << b.get(); } friend istream& operator>>(istream& is, mint& b) { int64_t val; is >> val; b = mint(val); return is; } }; using mint = MontgomeryModInt<998244353>; template struct binomial { vector _fac, _facInv; binomial(int size) : _fac(size), _facInv(size) { _fac[0] = 1; for(int i = 1; i < size; i++) _fac[i] = _fac[i - 1] * i; if (size > 0) _facInv.back() = 1 / _fac.back(); for(int i = size - 2; i >= 0; i--) _facInv[i] = _facInv[i + 1] * (i + 1); } Mint fac(int i) { return i < 0 ? 0 : _fac[i]; } Mint faci(int i) { return i < 0 ? 0 : _facInv[i]; } Mint binom(int n, int r) { return r < 0 or n < r ? 0 : fac(n) * faci(r) * faci(n - r); } }; template struct fenwickTree { const int size; vector data; fenwickTree(int _size) : size(_size + 1), data(_size + 1) {} fenwickTree(vector &init) : size(ssize(init) + 1), data(ssize(init) + 1) { partial_sum(init.begin(), init.end(), data.begin() + 1); for(int i = size - 1; i > 0; i--) data[i] -= data[i - (i & (-i))]; } void add(int i, T d) { for(i += 1; i < size; i += i & (-i)) data[i] += d; } T query(int i) { T res = T(0); for(i += 1; i > 0; i -= i & (-i)) res += data[i]; return res; } T query(int l, int r) { return query(r - 1) - query(l - 1); } }; signed main() { ios::sync_with_stdio(false), cin.tie(NULL); int n; cin >> n; vector p(n); for(int &x : p) { cin >> x; x--; } vector pos(n); for(int i = 0; i < n; i++) pos[p[i]] = i; mint ans = 0; fenwickTree ft(n); binomial bn(n); for(int v = 0; v < n; v++) { if (v > 0) ft.add(pos[v - 1], 1); int ld = ft.query(pos[v]); int rd = v - ld; int lu = pos[v] - ld; int ru = (n - 1) - ld - rd - lu; ans += bn.binom(ld + ru, max(ld, ru)) * bn.binom(lu + rd, max(lu, rd)); } cout << ans << '\n'; return 0; }