#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 #ifdef LOCAL # include "debug_print.hpp" # define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__) #else # define debug(...) (static_cast(0)) #endif using namespace std; #define rep1(a) for(int i = 0; i < a; i++) #define rep2(i, a) for(int i = 0; i < a; i++) #define rep3(i, a, b) for(int i = a; i < b; i++) #define rep4(i, a, b, c) for(int i = a; i < b; i += c) #define overload4(a, b, c, d, e, ...) e #define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__) #define rrep1(a) for(int i = (a)-1; i >= 0; i--) #define rrep2(i, a) for(int i = (a)-1; i >= 0; i--) #define rrep3(i, a, b) for(int i = (b)-1; i >= a; i--) #define rrep4(i, a, b, c) for(int i = (b)-1; i >= a; i -= c) #define rrep(...) overload4(__VA_ARGS__, rrep4, rrep3, rrep2, rrep1)(__VA_ARGS__) #define ALL(v) v.begin(), v.end() #define RALL(v) v.rbegin(), v.rend() #define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() ); #define pb push_back using ll = long long; using D = double; using LD = long double; using P = pair; using vi = vector; using vl = vector; template using vc = vector; template using vvc = vector>; template using vvvc = vector>; template using vvvvc = vector>; template using vvvvvc = vector>; #define vv(type, name, h, ...) \ vector> name(h, vector(__VA_ARGS__)) #define vvv(type, name, h, w, ...) \ vector>> name( \ h, vector>(w, vector(__VA_ARGS__))) #define vvvv(type, name, a, b, c, ...) \ vector>>> name( \ a, vector>>( \ b, vector>(c, vector(__VA_ARGS__)))) template using PQ = priority_queue>; template using minPQ = priority_queue, greater>; templatebool chmax(T &a, const T &b) { if (abool chmin(T &a, const T &b) { if (b ostream &operator<<(ostream &os, const pair &p) { os << p.first << " " << p.second; return os; } template istream &operator>>(istream &is, pair &p) { is >> p.first >> p.second; return is; } template ostream &operator<<(ostream &os, const vector &v) { int s = (int)v.size(); for (int i = 0; i < s; i++) os << (i ? " " : "") << v[i]; return os; } template istream &operator>>(istream &is, vector &v) { for (auto &x : v) is >> x; return is; } void in() {} template void in(T &t, U &...u) { cin >> t; in(u...); } void out() { cout << "\n"; } template void out(const T &t, const U &...u) { cout << t; if (sizeof...(u)) cout << sep; out(u...); } void outr() {} template void outr(const T &t, const U &...u) { cout << t; outr(u...); } template struct LazyMontgomeryModInt { using mint = LazyMontgomeryModInt; using i32 = int32_t; using u32 = uint32_t; using u64 = uint64_t; static constexpr u32 get_r() { u32 ret = mod; for (i32 i = 0; i < 4; ++i) ret *= 2 - mod * ret; return ret; } static constexpr u32 r = get_r(); static constexpr u32 n2 = -u64(mod) % mod; static_assert(mod < (1 << 30), "invalid, mod >= 2 ^ 30"); static_assert((mod & 1) == 1, "invalid, mod % 2 == 0"); static_assert(r * mod == 1, "this code has bugs."); u32 a; constexpr LazyMontgomeryModInt() : a(0) {} constexpr LazyMontgomeryModInt(const int64_t &b) : a(reduce(u64(b % mod + mod) * n2)){}; static constexpr u32 reduce(const u64 &b) { return (b + u64(u32(b) * u32(-r)) * mod) >> 32; } constexpr mint &operator+=(const mint &b) { if (i32(a += b.a - 2 * mod) < 0) a += 2 * mod; return *this; } constexpr mint &operator-=(const mint &b) { if (i32(a -= b.a) < 0) a += 2 * mod; return *this; } constexpr mint &operator*=(const mint &b) { a = reduce(u64(a) * b.a); return *this; } constexpr mint &operator/=(const mint &b) { *this *= b.inverse(); return *this; } constexpr mint operator+(const mint &b) const { return mint(*this) += b; } constexpr mint operator-(const mint &b) const { return mint(*this) -= b; } constexpr mint operator*(const mint &b) const { return mint(*this) *= b; } constexpr mint operator/(const mint &b) const { return mint(*this) /= b; } constexpr bool operator==(const mint &b) const { return (a >= mod ? a - mod : a) == (b.a >= mod ? b.a - mod : b.a); } constexpr bool operator!=(const mint &b) const { return (a >= mod ? a - mod : a) != (b.a >= mod ? b.a - mod : b.a); } constexpr mint operator-() const { return mint() - mint(*this); } constexpr mint operator+() const { return mint(*this); } constexpr mint pow(u64 n) const { mint ret(1), mul(*this); while (n > 0) { if (n & 1) ret *= mul; mul *= mul; n >>= 1; } return ret; } constexpr mint inverse() const { int x = get(), y = mod, u = 1, v = 0, t = 0, tmp = 0; while (y > 0) { t = x / y; x -= t * y, u -= t * v; tmp = x, x = y, y = tmp; tmp = u, u = v, v = tmp; } return mint{u}; } friend ostream &operator<<(ostream &os, const mint &b) { return os << b.get(); } friend istream &operator>>(istream &is, mint &b) { int64_t t; is >> t; b = LazyMontgomeryModInt(t); return (is); } constexpr u32 get() const { u32 ret = reduce(a); return ret >= mod ? ret - mod : ret; } static constexpr u32 get_mod() { return mod; } }; const int mod = 998244353; //const int mod = 1000000007; using mint = LazyMontgomeryModInt; #include "atcoder/lazysegtree.hpp" const ll INF = -1e18; struct S{ int len; ll sl, sr; mint slr; }; struct F{ ll lv, rv; }; S op(S a, S b) { return {a.len+b.len, a.sl+b.sl, a.sr+b.sr, a.slr+b.slr}; } S e() { return {0,0,0,0}; } S mapping(F f, S x) { if (f.lv == INF and f.rv == INF) return x; else if (f.lv == INF) return {x.len, x.sl, x.len*f.rv, mint(f.rv) * x.sl}; else if (f.rv == INF) return {x.len, x.len*f.lv, x.sr, mint(f.lv) * x.sr}; else return {x.len, x.len*f.lv, x.len*f.rv, mint(x.len) * f.lv * f.rv}; } F composition(F f, F g) { ll nl = (f.lv == INF ? g.lv : f.lv); ll nr = (f.rv == INF ? g.rv : f.rv); return {nl, nr}; } F id() { return {INF, INF}; } int main(){ ios_base::sync_with_stdio(false); cin.tie(nullptr); int n; in(n); vector a(n); in(a); vector init(n, {1,0,0,0}); atcoder::lazy_segtree seg(init); mint ans = a[0] * a[0]; seg.set(0, {1, a[0], a[0], a[0]*a[0]}); stack

stkl, stkr; stkl.emplace(a[0],0); stkr.emplace(a[0],0); rep(j,1,n){ while(!stkl.empty() and stkl.top().first > a[j]) stkl.pop(); while(!stkr.empty() and stkr.top().first < a[j]) stkr.pop(); if(a[j-1] > a[j]) { int i = stkl.empty() ? 0 : stkl.top().second + 1; ans += seg.prod(0,j).slr; auto spre = seg.prod(i,j); ans -= spre.slr; ans += mint(a[j]) * spre.sr; seg.apply(i,j, {a[j],INF}); } else{ int i = stkr.empty() ? 0 : stkr.top().second + 1; ans += seg.prod(0,j).slr; auto spre = seg.prod(i,j); ans -= spre.slr; ans += mint(a[j]) * spre.sl; seg.apply(i,j, {INF,a[j]}); } stkl.emplace(a[j], j); stkr.emplace(a[j], j); ans += a[j] * a[j]; seg.set(j,{1,a[j], a[j], a[j]*a[j]}); } out(ans); }