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

#include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
#include <bitset>    // bitset
#include <deque>     // deque
#include <iomanip>   //setprecsion
#include <iostream>  // cout, endl, cin
#include <iterator>  // std::back_inserter
#include <map>       // map
#include <queue>     // queue, priority_queue
#include <set>       // set
#include <stack>     // stack
#include <string>    // string, to_string, stoi
#include <tuple>     // tuple, make_tuple
#include <utility>   // pair, make_pair
#include <vector>    // vector

#include <cctype> // isupper, islower, isdigit, toupper, tolower
#include <cmath>  //sin, cos, tan

using namespace std;

#define rep(i, n) for (ll i = 0; i < (n); ++i)
#define alf(i) for (char i = 'a'; i < 'z'; ++i)
#define rrep(i, n) for (ll i = (n - 1); i >= 0; --i)
#define blank(ans) cout << (ans) << " ";
#define mp(p, q) make_pair(p, q)
#define mt(p, q, r) make_tuple(p, q, r)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef string str;

typedef vector<ll> vll;
typedef vector<ld> vd;
typedef vector<bool> vb;
typedef vector<char> vc;
typedef vector<str> vs;
typedef vector<vector<ll>> vvll;
typedef vector<vector<ld>> vvd;
typedef vector<vector<bool>> vvb;
typedef vector<vector<char>> vvc;
typedef vector<vector<str>> vvs;
typedef vector<pair<ll, ll>> vpll;
typedef vector<tuple<ll, ll, ll>> vtlll;

const ld PI = acos(-1.0);
const ll MAX = 9000000000000000000;
const ll MIN = -9000000000000000000;
const ld DMAX = 4500;
const ld DMIN = -4500;
const ll MOD = 1000000007;

template <typename T> void fin(T a) {
  cout << a << endl;
  exit(0);
}

void Main() {
  ll n;
  cin >> n;
  vll a(n), b(n);
  map<ll, ll> flag;
  ll ans = 0;
  rep(i, n) {
    ll A;
    cin >> A;
    a[i] = A + 1 + i;
    b[i] = i + 1 - A;
    if (flag.count(b[i]))
      flag[b[i]]++;
    else
      flag[b[i]] = 1;
  }
  reverse(all(a));
  rep(i, n) {
    if (flag.count(a[i]))
      ans += flag[a[i]];
  }
  fin(ans);
}

// 前処理
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(20); // 高精度少数表示
  // cout << setfill('0') << internal << setw(4); 0埋め４桁
  Main();
  return 0;
}


Error: TLE

Fixed submission:

#include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
#include <bitset>    // bitset
#include <deque>     // deque
#include <iomanip>   //setprecsion
#include <iostream>  // cout, endl, cin
#include <map>       // map
#include <queue>     // queue, priority_queue
#include <set>       // set
#include <stack>     // stack
#include <string>    // string, to_string, stoi
#include <tuple>     // tuple, make_tuple
#include <utility>   // pair, make_pair
#include <vector>    // vector

#include <cctype> // isupper, islower, isdigit, toupper, tolower
#include <cmath>  //sin, cos, tan

using namespace std;

#define rep(i, n) for (ll i = 0; i < (n); ++i)
#define rrep(i, n) for (ll i = (n - 1); i >= 0; --i)
#define blank(ans) cout << (ans) << " ";
#define mp(p, q) make_pair(p, q)
#define mt(p, q, r) make_tuple(p, q, r)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef string str;

typedef vector<ll> vll;
typedef vector<ld> vd;
typedef vector<bool> vb;
typedef vector<char> vc;
typedef vector<str> vs;
typedef vector<vector<ll>> vvll;
typedef vector<vector<ld>> vvd;
typedef vector<vector<bool>> vvb;
typedef vector<vector<char>> vvc;
typedef vector<vector<str>> vvs;
typedef vector<pair<ll, ll>> vpll;
typedef vector<tuple<ll, ll, ll>> vtlll;

const ld PI = acos(-1.0);
const ll MAX = 9000000000000000000;
const ll MIN = -9000000000000000000;
const ld DMAX = 4500;
const ld DMIN = -4500;
const ll MOD = 1000000007;

template <typename T> void fin(T a) {
  cout << a << endl;
  exit(0);
}

void Main() {
  ll n;
  cin >> n;
  vll a(n);
  rep(i, n) cin >> a[i];
  ll ans = 0;
  for (ll i = 0; i < n; i++) {
    for (ll j = i + 1; j < n; j++) {
      if (a[i] + a[j] == abs(i - j))
        ans++;
    }
  }
  fin(ans);
}

// 前処理
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(20); // 高精度少数表示
  // cout << setfill('0') << internal << setw(4); 0埋め４桁
  Main();
  return 0;
}