Problem p02691 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define REP(i, n) for (ll i = 0; i < (ll)n; i++)
#define REPR(i, n) for (ll i = (ll)n - 1; i >= 0; i--)
#define FOR(i, m, n) for (ll i = (ll)m; i < (ll)n; i++)
#define FORR(i, m, n) for (ll i = (ll)m - 1; i >= (ll)n; i--)
#define ALL(x) (x).begin(), (x).end()
#define ASC(v) sort(ALL(v));
#define DESC(v) sort(ALL(v), greater<int>());
#define UNIQ(a)                                                                \\
  sort(ALL(a));                                                                \\
  (a).resize(unique(ALL(a)) - a.begin());
#define PRINTD(x, d) cout << fixed << setprecision(d) << x << "\\n";
#define DEBUG(x) cout << #x << ": " << x << "\\n"
const double PI = acos(-1);
ll lcm(ll a, ll b) { return a / __gcd(a, b) * b; }
bool isprime(int x) {
  int i;
  if (x < 2)
    return 0;
  else if (x == 2)
    return 1;
  if (x % 2 == 0)
    return 0;
  for (i = 3; i * i <= x; i += 2)
    if (x % i == 0)
      return 0;
  return 1;
}
int digsum(int n) {
  int r = 0;
  while (n > 0) {
    r += n % 10;
    n /= 10;
  }
  return r;
}
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
struct nya {
  nya() {
    cin.tie(0);
    ios::sync_with_stdio(false);
  }
} nyan;

int main() {
  ll N;
  cin >> N;
  map<ll, ll> M;
  ll res = 0;
  REP(i, N) {
    ll x;
    cin >> x;
    res += M[i - x];
    M[i + x]++;
  }
  cout << res << "\\n";
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define REP(i, n) for (ll i = 0; i < (ll)n; i++)
#define REPR(i, n) for (ll i = (ll)n - 1; i >= 0; i--)
#define FOR(i, m, n) for (ll i = (ll)m; i < (ll)n; i++)
#define FORR(i, m, n) for (ll i = (ll)m - 1; i >= (ll)n; i--)
#define ALL(x) (x).begin(), (x).end()
#define ASC(v) sort(ALL(v));
#define DESC(v) sort(ALL(v), greater<int>());
#define UNIQ(a)                                                                \\
  sort(ALL(a));                                                                \\
  (a).resize(unique(ALL(a)) - a.begin());
#define PRINTD(x, d) cout << fixed << setprecision(d) << x << "\\n";
#define DEBUG(x) cout << #x << ": " << x << "\\n"
const double PI = acos(-1);
ll lcm(ll a, ll b) { return a / __gcd(a, b) * b; }
bool isprime(int x) {
  int i;
  if (x < 2)
    return 0;
  else if (x == 2)
    return 1;
  if (x % 2 == 0)
    return 0;
  for (i = 3; i * i <= x; i += 2)
    if (x % i == 0)
      return 0;
  return 1;
}
int digsum(int n) {
  int r = 0;
  while (n > 0) {
    r += n % 10;
    n /= 10;
  }
  return r;
}
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
struct nya {
  nya() {
    cin.tie(0);
    ios::sync_with_stdio(false);
  }
} nyan;

int main() {
  ll N;
  cin >> N;
  ll max = 0;
  vector<ll> A(N + 1);
  REP(i, N) {
    cin >> A[i + 1];
    chmax(max, A[i + 1]);
  }
  ll c = 0;
  FOR(i, 1, N + 1) {
    ll a = A[i];
    ll n = 2;
    FOR(j, i + 2, N + 1) {
      if (n == a + A[j])
        c++;
      n++;
      if (a + max < n)
        break;
    }
  }
  cout << c << "\\n";
}