#include using namespace std; using lint = long long; using pint = pair; using plint = pair; struct fast_ios { fast_ios(){ cin.tie(nullptr), ios::sync_with_stdio(false), cout << fixed << setprecision(20); }; } fast_ios_; #define ALL(x) (x).begin(), (x).end() #define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i=i##_begin_;i--) #define REP(i, n) FOR(i,0,n) #define IREP(i, n) IFOR(i,0,n) template void ndarray(vector& vec, const V& val, int len) { vec.assign(len, val); } template void ndarray(vector& vec, const V& val, int len, Args... args) { vec.resize(len), for_each(begin(vec), end(vec), [&](T& v) { ndarray(v, val, args...); }); } template bool chmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; } template bool chmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; } int floor_lg(long long x) { return x <= 0 ? -1 : 63 - __builtin_clzll(x); } template pair operator+(const pair &l, const pair &r) { return make_pair(l.first + r.first, l.second + r.second); } template pair operator-(const pair &l, const pair &r) { return make_pair(l.first - r.first, l.second - r.second); } template vector sort_unique(vector vec) { sort(vec.begin(), vec.end()), vec.erase(unique(vec.begin(), vec.end()), vec.end()); return vec; } template istream &operator>>(istream &is, vector &vec) { for (auto &v : vec) is >> v; return is; } template ostream &operator<<(ostream &os, const vector &vec) { os << '['; for (auto v : vec) os << v << ','; os << ']'; return os; } template ostream &operator<<(ostream &os, const array &arr) { os << '['; for (auto v : arr) os << v << ','; os << ']'; return os; } #if __cplusplus >= 201703L template istream &operator>>(istream &is, tuple &tpl) { std::apply([&is](auto &&... args) { ((is >> args), ...);}, tpl); return is; } template ostream &operator<<(ostream &os, const tuple &tpl) { std::apply([&os](auto &&... args) { ((os << args << ','), ...);}, tpl); return os; } #endif template ostream &operator<<(ostream &os, const deque &vec) { os << "deq["; for (auto v : vec) os << v << ','; os << ']'; return os; } template ostream &operator<<(ostream &os, const set &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; } template ostream &operator<<(ostream &os, const unordered_set &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; } template ostream &operator<<(ostream &os, const multiset &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; } template ostream &operator<<(ostream &os, const unordered_multiset &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; } template ostream &operator<<(ostream &os, const pair &pa) { os << '(' << pa.first << ',' << pa.second << ')'; return os; } template ostream &operator<<(ostream &os, const map &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; } template ostream &operator<<(ostream &os, const unordered_map &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; } #ifdef HITONANODE_LOCAL const string COLOR_RESET = "\033[0m", BRIGHT_GREEN = "\033[1;32m", BRIGHT_RED = "\033[1;31m", BRIGHT_CYAN = "\033[1;36m", NORMAL_CROSSED = "\033[0;9;37m", RED_BACKGROUND = "\033[1;41m", NORMAL_FAINT = "\033[0;2m"; #define dbg(x) cerr << BRIGHT_CYAN << #x << COLOR_RESET << " = " << (x) << NORMAL_FAINT << " (L" << __LINE__ << ") " << __FILE__ << COLOR_RESET << endl #else #define dbg(x) (x) #endif // 0-indexed BIT (binary indexed tree / Fenwick tree) (i : [0, len)) template struct BIT { int n; std::vector data; BIT(int len = 0) : n(len), data(len) {} void reset() { std::fill(data.begin(), data.end(), T(0)); } void add(int pos, T v) { // a[pos] += v pos++; while (pos > 0 and pos <= n) data[pos - 1] += v, pos += pos & -pos; } T sum(int k) const { // a[0] + ... + a[k - 1] T res = 0; while (k > 0) res += data[k - 1], k -= k & -k; return res; } T sum(int l, int r) const { return sum(r) - sum(l); } // a[l] + ... + a[r - 1] friend std::ostream &operator<<(std::ostream &os, const BIT &bit) { T prv = 0; os << '['; for (int i = 1; i <= bit.n; i++) { T now = bit.sum(i); os << now - prv << ',', prv = now; } return os << ']'; } }; int main() { int N; cin >> N; vector A(N); cin >> A; for (auto &a : A) a--; vector pos(N); REP(i, N) pos[A[i]] = i; BIT bit(N + 1); vector lohi(N); vector> bg(N + 1), ed(N + 1); REP(i, N) { bool md = false; int lo = 0, hi = N; if (i == 0) { md = (A[i + 1] < A[i]); } else { md = (A[i - 1] < A[i]); } if (md) { hi = N; if (i) chmax(lo, A[i - 1] + 1); if (i + 1 < N) chmax(lo, A[i + 1] + 1); } else { lo = 0; if (i) chmin(hi, A[i - 1]); if (i + 1 < N) chmin(hi, A[i + 1]); } lohi[i] = make_pair(lo, hi); bg[lo].push_back(A[i]); ed[hi].push_back(A[i]); } dbg(lohi); lint ret = 0; REP(a, N) { for (auto b : bg[a]) { bit.add(b, 1); } for (auto b : ed[a]) { bit.add(b, -1); } auto [l, r] = lohi[pos[a]]; ret += bit.sum(l, r); } cout << (ret - N) / 2 << '\n'; }