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

#include <bits/stdc++.h>
typedef long long ll;
using namespace std;
ll MOD = 1000000007;

#define vec vector<int>
#define vecll vector<ll>
#define vecst vector<string>
#define vecb vector<bool>
#define vec2(var, n, m) vector<vector<int>> var(n, vector<int>(m, 0))
#define vecll2(var, n, m) vector<vector<ll>> var(n, vector<ll>(m, 0))

#define rep(i, n) for (ll i = (ll)0; i < (ll)n; i++)
#define REP(i, m, n) for (ll i = (ll)m; i < (ll)n; i++)
#define arr(var, n)                                                            \\
  vec var(n);                                                                  \\
  rep(i, n) { cin >> var[i]; }
#define arrll(var, n)                                                          \\
  vecll var(n);                                                                \\
  rep(i, n) { cin >> var[i]; }
#define arrst(var, n)                                                          \\
  vecst var(n);                                                                \\
  rep(i, n) { cin >> var[i]; }
#define all(var) (var).begin(), (var).end()
#define sortall(var) sort(all(var))
#define uniqueall(v) v.erase(unique(v.begin(), v.end()), v.end());
#define f_sum(var) accumulate(all(var), 0)
#define f_sumll(var) accumulate(all(var), 0LL)
#define chmin(v1, v2) v1 = min(v1, v2)
#define chmax(v1, v2) v1 = max(v1, v2)
#define mp(v1, v2) make_pair(v1, v2)
#define pb(var) push_back(var)
#define prt(var) cout << (var) << "\\n"
#define prtd(n, var) cout << fixed << setprecision(n) << var << "\\n"
#define prtfill(n, var) cout << setw(n) << setfill('0') << var;
#define prt2(v1, v2) cout << v1 << " " << v2 << "\\n"
#define prt3(v1, v2, v3) cout << v1 << " " << v2 << " " << v3 << "\\n"
#define prtall(v)                                                              \\
  rep(i, v.size()) { cout << v[i] << (i != v.size() - 1 ? " " : "\\n"); }
void prtok(bool ok) { prt(ok ? "yes" : "no"); }
//----------------------------------------------------------------

int main(void) {
  int n;
  cin >> n;
  arrll(a, n);

  map<ll, ll> mpL, mpR;
  rep(i, n) {
    ll l = i + 1 + a[i];
    ll r = i + 1 - a[i];

    if (mpL.find(l) == mpL.end()) {
      mpL.emplace(l, 1);
    } else {
      mpL[l]++;
    }

    if (mpR.find(r) == mpR.end()) {
      mpR.emplace(r, 1);
    } else {
      mpR[r]++;
    }
  }

  ll ans = 0;
  for (auto itr : mpL) {
    if (mpR.find(itr.first) != mpR.end()) {
      ans += itr.second * mpR[itr.first];
    }
  }

  prt(ans);
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
typedef long long ll;
using namespace std;
ll MOD = 1e9 + 7;

#define vec vector<int>
#define vecll vector<ll>
#define vec2 vector<vector<int>>
#define vec2ll vector<vector<ll>>
#define vpair vector<pair<int, int>>
#define vpairll vector<pair<ll, ll>>
#define vecst vector<string>
#define vecb vector<bool>

#define rep(i, n) for (ll i = (ll)0; i < (ll)n; i++)
#define REP(i, m, n) for (ll i = (ll)m; i < (ll)n; i++)
#define arr(var, n)                                                            \\
  vec var(n);                                                                  \\
  rep(i, n) { cin >> var[i]; }
#define arrll(var, n)                                                          \\
  vecll var(n);                                                                \\
  rep(i, n) { cin >> var[i]; }
#define arrst(var, n)                                                          \\
  vecst var(n);                                                                \\
  rep(i, n) { cin >> var[i]; }
#define all(var) (var).begin(), (var).end()
#define sortall(var) sort(all(var))
#define uniqueall(v) v.erase(unique(v.begin(), v.end()), v.end());
#define f_sum(var) accumulate(all(var), 0)
#define f_sumll(var) accumulate(all(var), 0LL)
#define chmin(v1, v2) v1 = min(v1, v2)
#define chmax(v1, v2) v1 = max(v1, v2)
#define mpair(v1, v2) make_pair(v1, v2)
#define pb(var) push_back(var)
#define prt(var) cout << var << "\\n"
#define prtd(n, var) cout << fixed << setprecision(n) << var << "\\n"
#define prtfill(n, var) cout << setw(n) << setfill('0') << var;
#define prt2(v1, v2) cout << v1 << " " << v2 << "\\n"
#define prt3(v1, v2, v3) cout << v1 << " " << v2 << " " << v3 << "\\n"
#define prtall(v)                                                              \\
  rep(i, v.size()) { cout << v[i] << (i != v.size() - 1 ? " " : "\\n"); }
void prtok(bool ok) { prt((ok ? "Yes" : "No")); }
//----------------------------------------------------------------

int main(void) {
  int n;
  cin >> n;
  arrll(a, n);

  ll ans = 0;
  rep(i, n) {
    for (ll j = i + a[i]; (j > i && j < n); j++) {
      if (a[i] + a[j] == abs(i - j))
        ans++;
    }
  }

  prt(ans);
}