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

/**
 * Includes
 */
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <vector>

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

using namespace std;

/**
 * Macros
 */
#define rep(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define repx(i, s, e, d) for (int i = s, i##_end = (e); i < i##_end; i += d)
#define repxr(i, s, e, d) for (int i = s, i##_end = (e); i > i##_end; i += d)
#define rept(n)                                                                \\
  for (int ___i___ = 0, i##_len = (n); ___i___ < i##_len; ++___i___)
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define ZERO(a) memset(a, 0, sizeof(a))
#define BIT(n) (1LL << (n))
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());
#define CEIL(x, y) (((x) + ((x) > 0 ? (y)-1 : -((y)-1))) / (y))

/**
 * Standard input helpers
 */
// vector:input
template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec)
    is >> x;
  return is;
}
// pair:output
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}
// vector:output
template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << "{";
  for (int i = 0; i < vec.size(); i++) {
    os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
  }
  os << "}";
  return os;
}
// map:output
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  os << "{";
  repi(itr, map_var) {
    os << *itr;
    itr++;
    if (itr != map_var.end())
      os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
// set:output
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  os << "{";
  repi(itr, set_var) {
    os << *itr;
    itr++;
    if (itr != set_var.end())
      os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
/**
 * Debug tools
 */
#define DUMPOUT cout
void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) > 0) {
    DUMPOUT << ", ";
  }
  dump_func(std::move(tail)...);
}
#ifdef LOCAL_
#define dump(...)                                                              \\
  DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                              \\
          << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" << endl  \\
          << "    ",                                                           \\
      dump_func(__VA_ARGS__)
#else
#define dump(...)
#endif

/**
 * Helpers
 */
using lli = long long int;
using ii = pair<int, int>;
template <typename T>
using heapq = priority_queue<T, vector<T>, greater<T>>; // implement <
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
int exdx[8] = {1, 1, 1, 0, 0, -1, -1, -1};
int exdy[8] = {1, 0, -1, 1, -1, 1, 0, -1};
struct aaa {
  aaa() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(20);
  };
} aaaaaaa;
/**
 * Libraries
 */
// (paste function or Libraries from ContestLibrary)
/**
 * If necessary
 */
#define int long long int
// #define INF (1e9 + 1)
/**
 * Solver
 */
signed main() {
  int N;
  cin >> N;
  vector<int> A(N);
  cin >> A;
  vector<int> b(N);
  rep(i, N) { b[i] = (i + 1) - A[i]; }
  sort(ALL(b));

  int ans = 0;
  rep(i, N) {
    int ai_i = (i + 1) + A[i];
    auto low = lower_bound(ALL(b), ai_i);
    auto up = upper_bound(ALL(b), ai_i);
    ans += (int)(up - low);
  }
  cout << ans << endl;
  return 0;
}


Error: TLE

Fixed submission:

/**
 * Includes
 */
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <vector>

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

using namespace std;

/**
 * Macros
 */
#define rep(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define repx(i, s, e, d) for (int i = s, i##_end = (e); i < i##_end; i += d)
#define repxr(i, s, e, d) for (int i = s, i##_end = (e); i > i##_end; i += d)
#define rept(n)                                                                \\
  for (int ___i___ = 0, i##_len = (n); ___i___ < i##_len; ++___i___)
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define ZERO(a) memset(a, 0, sizeof(a))
#define BIT(n) (1LL << (n))
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());
#define CEIL(x, y) (((x) + ((x) > 0 ? (y)-1 : -((y)-1))) / (y))

/**
 * Standard input helpers
 */
// vector:input
template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec)
    is >> x;
  return is;
}
// pair:output
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}
// vector:output
template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << "{";
  for (int i = 0; i < vec.size(); i++) {
    os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
  }
  os << "}";
  return os;
}
// map:output
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  os << "{";
  repi(itr, map_var) {
    os << *itr;
    itr++;
    if (itr != map_var.end())
      os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
// set:output
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  os << "{";
  repi(itr, set_var) {
    os << *itr;
    itr++;
    if (itr != set_var.end())
      os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
/**
 * Debug tools
 */
#define DUMPOUT cout
void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) > 0) {
    DUMPOUT << ", ";
  }
  dump_func(std::move(tail)...);
}
#ifdef LOCAL_
#define dump(...)                                                              \\
  DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                              \\
          << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" << endl  \\
          << "    ",                                                           \\
      dump_func(__VA_ARGS__)
#else
#define dump(...)
#endif

/**
 * Helpers
 */
using lli = long long int;
using ii = pair<int, int>;
template <typename T>
using heapq = priority_queue<T, vector<T>, greater<T>>; // implement <
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
int exdx[8] = {1, 1, 1, 0, 0, -1, -1, -1};
int exdy[8] = {1, 0, -1, 1, -1, 1, 0, -1};
struct aaa {
  aaa() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(20);
  };
} aaaaaaa;
/**
 * Libraries
 */
// (paste function or Libraries from ContestLibrary)
/**
 * If necessary
 */
// #define int long long int
// #define INF (1e9 + 1)
/**
 * Solver
 */
signed main() {
  int N;
  cin >> N;
  vector<int> A(N);
  cin >> A;
  vector<ii> b(N); // tall code
  rep(i, N) { b[i] = ii((i + 1) - A[i], i); }
  sort(ALL(b));

  set<ii> ans;
  rep(i, N) {
    int ai_i = (i + 1) + A[i];
    auto it = lower_bound(ALL(b), ii(ai_i, 0));
    for (; it != b.end(); ++it) {
      int j = it->second;
      if (abs(i - j) == A[i] + A[j]) {
        ans.insert(ii(i + 1, j + 1));
      }
    }
  }
  cout << SZ(ans) << endl;
  return 0;
}