Problem p02650 (C++)

Buggy submission (status: Time Limit Exceeded):
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")

#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
#define SZ(x) ((int)((x).size()))

template <typename T1, typename T2>
string print_iterable(T1 begin_iter, T2 end_iter, int counter) {
  bool done_something = false;
  stringstream res;
  res << "[";
  for (; begin_iter != end_iter and counter; ++begin_iter) {
    done_something = true;
    counter--;
    res << *begin_iter << ", ";
  }
  string str = res.str();
  if (done_something) {
    str.pop_back();
    str.pop_back();
  }
  str += "]";
  return str;
}

vector<int> SortIndex(int size, std::function<bool(int, int)> compare) {
  vector<int> ord(size);
  for (int i = 0; i < size; i++)
    ord[i] = i;
  sort(ord.begin(), ord.end(), compare);
  return ord;
}

template <typename T> bool MinPlace(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T> bool MaxPlace(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <typename S, typename T>
ostream &operator<<(ostream &out, const pair<S, T> &p) {
  out << "{" << p.first << ", " << p.second << "}";
  return out;
}

template <typename T> ostream &operator<<(ostream &out, const vector<T> &v) {
  out << "[";
  for (int i = 0; i < (int)v.size(); i++) {
    out << v[i];
    if (i != (int)v.size() - 1)
      out << ", ";
  }
  out << "]";
  return out;
}

template <class TH> void _dbg(const char *name, TH val) {
  clog << name << ": " << val << endl;
}
template <class TH, class... TA>
void _dbg(const char *names, TH curr_val, TA... vals) {
  while (*names != ',')
    clog << *names++;
  clog << ": " << curr_val << ", ";
  _dbg(names + 1, vals...);
}

#if DEBUG && !ONLINE_JUDGE
ifstream input_from_file("input.txt");
#define cin input_from_file

#define dbg(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define dbg_arr(x, len)                                                        \
  clog << #x << ": " << print_iterable(x, x + len, -1) << endl;
#else
#define dbg(...)
#define dbg_arr(x, len)
#endif

///////////////////////////////////////////////////////////////////////////
//////////////////// DO NOT TOUCH BEFORE THIS LINE ////////////////////////
///////////////////////////////////////////////////////////////////////////

LL solve(int W, int H, int K) {
  vector<int> preg(W);
  for (int i = 0; i < W; i++)
    preg[i] = __gcd(i, H);

  LL res = 0;
  for (int y = 1; y < H; y++) {
    for (int x1 = 1; x1 < W; x1++) {
      if ((H - y) * x1 > 2 * K + 2 * H)
        break;
      LL U = 2 * K - (H - y) * x1;
      if (((LL)y) * x1 <= U) {
        res += 2 * (x1 - 1) + 1;
        continue;
      }
      int low = 1;
      if (y <= U) {
        low = U / y;
        res += 2 * (low - 1);
      }
      int g = __gcd(x1, y);
      for (int x2 = low; x2 <= x1; x2++) {
        if (x1 != x2 and y * x2 > 2 * K + g + min(x2, H - y) + min(x1 - x2, H))
          x2 = x1;
        if ((LL)y * x2 > 1e6)
          break;
        LL c =
            (H - y) * x1 + y * x2 - (g + __gcd(x2, H - y) + preg[x1 - x2]) + 2;
        if (c <= 2 * K)
          res += (x1 != x2) ? 2 : 1;
      }
    }
  }
  return res;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0); // Remove in problems with online queries!

  int W, H, K;
  cin >> W >> H >> K;
  LL ris1 = solve(W, H, K);
  LL ris2 = solve(H, W, K);
  cout << 2 * (ris1 + ris2) << endl;
}


Fixed submission:
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")

#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
#define SZ(x) ((int)((x).size()))

template <typename T1, typename T2>
string print_iterable(T1 begin_iter, T2 end_iter, int counter) {
  bool done_something = false;
  stringstream res;
  res << "[";
  for (; begin_iter != end_iter and counter; ++begin_iter) {
    done_something = true;
    counter--;
    res << *begin_iter << ", ";
  }
  string str = res.str();
  if (done_something) {
    str.pop_back();
    str.pop_back();
  }
  str += "]";
  return str;
}

vector<int> SortIndex(int size, std::function<bool(int, int)> compare) {
  vector<int> ord(size);
  for (int i = 0; i < size; i++)
    ord[i] = i;
  sort(ord.begin(), ord.end(), compare);
  return ord;
}

template <typename T> bool MinPlace(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T> bool MaxPlace(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <typename S, typename T>
ostream &operator<<(ostream &out, const pair<S, T> &p) {
  out << "{" << p.first << ", " << p.second << "}";
  return out;
}

template <typename T> ostream &operator<<(ostream &out, const vector<T> &v) {
  out << "[";
  for (int i = 0; i < (int)v.size(); i++) {
    out << v[i];
    if (i != (int)v.size() - 1)
      out << ", ";
  }
  out << "]";
  return out;
}

template <class TH> void _dbg(const char *name, TH val) {
  clog << name << ": " << val << endl;
}
template <class TH, class... TA>
void _dbg(const char *names, TH curr_val, TA... vals) {
  while (*names != ',')
    clog << *names++;
  clog << ": " << curr_val << ", ";
  _dbg(names + 1, vals...);
}

#if DEBUG && !ONLINE_JUDGE
ifstream input_from_file("input.txt");
#define cin input_from_file

#define dbg(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define dbg_arr(x, len)                                                        \
  clog << #x << ": " << print_iterable(x, x + len, -1) << endl;
#else
#define dbg(...)
#define dbg_arr(x, len)
#endif

///////////////////////////////////////////////////////////////////////////
//////////////////// DO NOT TOUCH BEFORE THIS LINE ////////////////////////
///////////////////////////////////////////////////////////////////////////

LL solve(int W, int H, int K) {
  vector<int> preg(W);
  for (int i = 0; i < W; i++)
    preg[i] = __gcd(i, H);

  LL res = 0;
  for (int y = 1; y < H; y++) {
    for (int x1 = 1; x1 < W; x1++) {
      if ((H - y) * x1 > 2 * K + 2 * H)
        break;
      LL U = 2 * K - (H - y) * x1;
      if (((LL)y) * x1 <= U) {
        res += 2 * (x1 - 1) + 1;
        continue;
      }
      int low = 1;
      if (y <= U) {
        low = U / y;
        res += 2 * (low - 1);
      }
      int g = __gcd(x1, y);
      for (int x2 = low; x2 <= x1; x2++) {
        if (x1 != x2 and (H - y) * x1 + y * x2 >
                             2 * K + g + min(x2, H - y) + min(x1 - x2, H))
          x2 = x1;
        if ((LL)y * x2 > 1e6)
          break;
        LL c =
            (H - y) * x1 + y * x2 - (g + __gcd(x2, H - y) + preg[x1 - x2]) + 2;
        if (c <= 2 * K)
          res += (x1 != x2) ? 2 : 1;
      }
    }
  }
  return res;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0); // Remove in problems with online queries!

  int W, H, K;
  cin >> W >> H >> K;
  LL ris1 = solve(W, H, K);
  LL ris2 = solve(H, W, K);
  cout << 2 * (ris1 + ris2) << endl;
}