Problem p02919 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vb = vector<bool>;
using vvb = vector<vb>;
using vd = vector<double>;
using vvd = vector<vd>;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using tll = tuple<ll, ll>;
using tlll = tuple<ll, ll, ll>;
using vs = vector<string>;

#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define rep(i, n) range(i, 0, n)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
#define range(i, a, n) for (int i = (a); i < (n); i++)

#define LINF ((ll)1ll << 60)
#define INF ((int)1 << 30)
#define EPS (1e-9)
#define MOD (1000000007ll)
#define fcout(a) cout << setprecision(a) << fixed
#define fs first
#define sc second
#define PI 3.1415926535897932384

int dx[] = {1, 0, -1, 0, 1, -1, -1, 1}, dy[] = {0, 1, 0, -1, 1, 1, -1, -1};

template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class S> S acm(vector<S> &a) { return accumulate(all(a), S()); }
template <class S> S max(vector<S> &a) { return *max_element(all(a)); }
template <class S> S min(vector<S> &a) { return *min_element(all(a)); }
void YN(bool b) { cout << (b ? "YES" : "NO") << "\n"; }
void Yn(bool b) { cout << (b ? "Yes" : "No") << "\n"; }
void yn(bool b) { cout << (b ? "yes" : "no") << "\n"; }
int sgn(const double &r) { return (r > EPS) - (r < -EPS); } // a>0  : sgn(a)>0
int sgn(const double &a, const double &b) {
  return sgn(a - b);
} // b<=c : sgn(b,c)<=0

ll max(int a, ll b) { return max((ll)a, b); }
ll max(ll a, int b) { return max(a, (ll)b); }
template <class T> void puta(T &&t) { cout << t << "\n"; }
template <class H, class... T> void puta(H &&h, T &&...t) {
  cout << h << ' ';
  puta(t...);
}
template <class S, class T> ostream &operator<<(ostream &os, pair<S, T> p) {
  os << "[" << p.first << ", " << p.second << "]";
  return os;
};
template <class S> auto &operator<<(ostream &os, vector<S> t) {
  bool a = 1;
  for (auto s : t) {
    os << (a ? "" : " ") << s;
    a = 0;
  }
  return os;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  multiset<ll> s;
  ll n, ans = 0;
  cin >> n;
  vl v(n), ind(n);
  rep(i, n) cin >> v[i], ind[v[i] - 1] = i + 1;
  s.insert(0);
  s.insert(0);
  s.insert(n + 1);
  s.insert(n + 1);
  rrep(i, n) {
    ll num = ind[i];
    auto rl = lower_bound(all(s), num);
    auto rr = rl;
    auto ll = rl;
    auto lr = rl;
    rr++;
    lr--;
    ll--;
    ll--;
    ans += (i + 1) * (*lr - *ll) * (*rl - num);
    ans += (i + 1) * (num - *lr) * (*rr - *rl);
    s.insert(num);
  }
  puta(ans);
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vb = vector<bool>;
using vvb = vector<vb>;
using vd = vector<double>;
using vvd = vector<vd>;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using tll = tuple<ll, ll>;
using tlll = tuple<ll, ll, ll>;
using vs = vector<string>;

#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define rep(i, n) range(i, 0, n)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
#define range(i, a, n) for (int i = (a); i < (n); i++)

#define LINF ((ll)1ll << 60)
#define INF ((int)1 << 30)
#define EPS (1e-9)
#define MOD (1000000007ll)
#define fcout(a) cout << setprecision(a) << fixed
#define fs first
#define sc second
#define PI 3.1415926535897932384

int dx[] = {1, 0, -1, 0, 1, -1, -1, 1}, dy[] = {0, 1, 0, -1, 1, 1, -1, -1};

template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class S> S acm(vector<S> &a) { return accumulate(all(a), S()); }
template <class S> S max(vector<S> &a) { return *max_element(all(a)); }
template <class S> S min(vector<S> &a) { return *min_element(all(a)); }
void YN(bool b) { cout << (b ? "YES" : "NO") << "\n"; }
void Yn(bool b) { cout << (b ? "Yes" : "No") << "\n"; }
void yn(bool b) { cout << (b ? "yes" : "no") << "\n"; }
int sgn(const double &r) { return (r > EPS) - (r < -EPS); } // a>0  : sgn(a)>0
int sgn(const double &a, const double &b) {
  return sgn(a - b);
} // b<=c : sgn(b,c)<=0

ll max(int a, ll b) { return max((ll)a, b); }
ll max(ll a, int b) { return max(a, (ll)b); }
template <class T> void puta(T &&t) { cout << t << "\n"; }
template <class H, class... T> void puta(H &&h, T &&...t) {
  cout << h << ' ';
  puta(t...);
}
template <class S, class T> ostream &operator<<(ostream &os, pair<S, T> p) {
  os << "[" << p.first << ", " << p.second << "]";
  return os;
};
template <class S> auto &operator<<(ostream &os, vector<S> t) {
  bool a = 1;
  for (auto s : t) {
    os << (a ? "" : " ") << s;
    a = 0;
  }
  return os;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  multiset<ll> s;
  ll n, ans = 0;
  cin >> n;
  vl v(n), ind(n);
  rep(i, n) cin >> v[i], ind[v[i] - 1] = i + 1;
  s.insert(0);
  s.insert(0);
  s.insert(n + 1);
  s.insert(n + 1);
  rrep(i, n) {
    ll num = ind[i];
    auto rl = s.lower_bound(num);
    auto rr = rl;
    auto ll = rl;
    auto lr = rl;
    rr++;
    lr--;
    ll--;
    ll--;
    ans += (i + 1) * (*lr - *ll) * (*rl - num);
    ans += (i + 1) * (num - *lr) * (*rr - *rl);
    s.insert(num);
  }
  puta(ans);
}