Problem p03008 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define REP(i, n) for (long long i = 0, max_i = (n); i < max_i; i++)
#define REPI(i, a, b) for (long long i = (a), max_i = (b); i < max_i; i++)
#define ALL(obj) begin(obj), end(obj)
#define RALL(obj) rbegin(obj), rend(obj)
#define fi first
#define se second
using ii = pair<int, int>;
vector<ii> dirs = {
    {1, 0}, {0, 1},  {-1, 0},  {0, -1}, // 4方向
    {1, 1}, {-1, 1}, {-1, -1}, {1, -1}, // 斜め
    {0, 0},                             // 自身
};
template <class T> inline bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T, class S> vector<T> make_vec(size_t n, S x) {
  return vector<T>(n, x);
}
template <class T, class... Ts> auto make_vec(size_t n, Ts... ts) {
  return vector<decltype(make_vec<T>(ts...))>(n, make_vec<T>(ts...));
}

// debug
template <class T> ostream &operator<<(ostream &s, vector<T> &d) {
  REP(i, d.size()) s << d[i] << (i == d.size() - 1 ? "" : " ");
  return s;
}
template <class T> ostream &operator<<(ostream &s, vector<vector<T>> &d) {
  REP(i, d.size()) s << d[i] << (i == d.size() - 1 ? "" : "\n");
  return s;
}
template <class T, class S> ostream &operator<<(ostream &s, pair<T, S> &p) {
  s << "{" << p.first << ", " << p.second << "}";
  return s;
}
template <class T, class S> ostream &operator<<(ostream &s, map<T, S> m) {
  for (auto it = m.begin(); it != m.end(); it++) {
    s << *it << (next(it) == m.end() ? "" : "\n");
  }
  return s;
}
template <class T, class S>
ostream &operator<<(ostream &s, unordered_map<T, S> m) {
  for (auto it = m.begin(); it != m.end(); it++) {
    s << *it << (next(it) == m.end() ? "" : "\n");
  }
  return s;
}
#ifdef _MY_DEBUG
#define dump(...)                                                              \
  cerr << "/* " << #__VA_ARGS__ << " :[" << __LINE__ << ":" << __FUNCTION__    \
       << "]" << endl,                                                         \
      dump_func(__VA_ARGS__), cerr << "*/\n\n";
#else
#define dump(...)
#define endl "\n"
#endif
void dump_func() { cerr << endl; }
template <class Head, class... Tail> void dump_func(Head &&h, Tail &&...t) {
  cerr << h << (sizeof...(Tail) == 0 ? "" : ", "),
      dump_func(forward<Tail>(t)...);
}

struct Fast {
  Fast() {
    cin.tie(0);
    ios::sync_with_stdio(false);
  }
} fast;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
constexpr int MOD = 1000000007;
// *************** TEMPLATE END ***************

signed main() {
  int n;
  cin >> n;
  int xa, ya, za;
  cin >> xa >> ya >> za;
  int xb, yb, zb;
  cin >> xb >> yb >> zb;

  int ans1 = n;
  REP(n1, (xb > xa ? n + 1 : 1)) {
    REP(n2, (yb > ya ? n + 1 : 1)) {
      int n3 = n - n1 - n2;
      if (n3 < 0)
        break;
      chmax(ans1, n + n1 / xa * (xb - xa) + n2 / ya * (yb - ya) +
                      n3 / za * (zb - za));
    }
  }
  dump(ans1);

  swap(xa, xb);
  swap(ya, yb);
  swap(za, zb);

  int ans2 = ans1;
  REP(n1, (xb > xa ? ans1 + 1 : 1)) {
    REP(n2, (yb > ya ? ans1 + 1 : 1)) {
      int n3 = ans1 - n1 - n2;
      if (n3 < 0)
        break;
      chmax(ans2, ans1 + n1 / xa * (xb - xa) + n2 / ya * (yb - ya) +
                      n3 / za * (zb - za));
    }
  }
  cout << ans2 << endl;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define REP(i, n) for (long long i = 0, max_i = (n); i < max_i; i++)
#define REPI(i, a, b) for (long long i = (a), max_i = (b); i < max_i; i++)
#define ALL(obj) begin(obj), end(obj)
#define RALL(obj) rbegin(obj), rend(obj)
#define fi first
#define se second
using ii = pair<int, int>;
vector<ii> dirs = {
    {1, 0}, {0, 1},  {-1, 0},  {0, -1}, // 4方向
    {1, 1}, {-1, 1}, {-1, -1}, {1, -1}, // 斜め
    {0, 0},                             // 自身
};
template <class T> inline bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T, class S> vector<T> make_vec(size_t n, S x) {
  return vector<T>(n, x);
}
template <class T, class... Ts> auto make_vec(size_t n, Ts... ts) {
  return vector<decltype(make_vec<T>(ts...))>(n, make_vec<T>(ts...));
}

// debug
template <class T> ostream &operator<<(ostream &s, vector<T> &d) {
  REP(i, d.size()) s << d[i] << (i == d.size() - 1 ? "" : " ");
  return s;
}
template <class T> ostream &operator<<(ostream &s, vector<vector<T>> &d) {
  REP(i, d.size()) s << d[i] << (i == d.size() - 1 ? "" : "\n");
  return s;
}
template <class T, class S> ostream &operator<<(ostream &s, pair<T, S> &p) {
  s << "{" << p.first << ", " << p.second << "}";
  return s;
}
template <class T, class S> ostream &operator<<(ostream &s, map<T, S> m) {
  for (auto it = m.begin(); it != m.end(); it++) {
    s << *it << (next(it) == m.end() ? "" : "\n");
  }
  return s;
}
template <class T, class S>
ostream &operator<<(ostream &s, unordered_map<T, S> m) {
  for (auto it = m.begin(); it != m.end(); it++) {
    s << *it << (next(it) == m.end() ? "" : "\n");
  }
  return s;
}
#ifdef _MY_DEBUG
#define dump(...)                                                              \
  cerr << "/* " << #__VA_ARGS__ << " :[" << __LINE__ << ":" << __FUNCTION__    \
       << "]" << endl,                                                         \
      dump_func(__VA_ARGS__), cerr << "*/\n\n";
#else
#define dump(...)
#define endl "\n"
#endif
void dump_func() { cerr << endl; }
template <class Head, class... Tail> void dump_func(Head &&h, Tail &&...t) {
  cerr << h << (sizeof...(Tail) == 0 ? "" : ", "),
      dump_func(forward<Tail>(t)...);
}

struct Fast {
  Fast() {
    cin.tie(0);
    ios::sync_with_stdio(false);
  }
} fast;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
constexpr int MOD = 1000000007;
// *************** TEMPLATE END ***************

signed main() {
  int n;
  cin >> n;
  int xa, ya, za;
  cin >> xa >> ya >> za;
  int xb, yb, zb;
  cin >> xb >> yb >> zb;

  int ans1 = n;
  REP(n1, (xb > xa ? n + 1 : 1)) {
    REP(n2, (yb > ya ? n + 1 : 1)) {
      int n3 = n - n1 - n2;
      if (n3 < 0)
        break;
      chmax(ans1, n + n1 / xa * (xb - xa) + n2 / ya * (yb - ya) +
                      n3 / za * (zb - za));
    }
  }
  dump(ans1);

  swap(xa, xb);
  swap(ya, yb);
  swap(za, zb);

  int ans2 = ans1;
  if (xb > xa && yb > ya && zb < za) {
    REP(n1, ans1 + 1) {
      int n2 = ans1 - n1;
      chmax(ans2, ans1 + n1 / xa * (xb - xa) + n2 / ya * (yb - ya));
    }
  } else {
    REP(n1, (xb > xa ? ans1 + 1 : 1)) {
      REP(n2, (yb > ya ? ans1 + 1 : 1)) {
        int n3 = ans1 - n1 - n2;
        if (n3 < 0)
          break;
        chmax(ans2, ans1 + n1 / xa * (xb - xa) + n2 / ya * (yb - ya) +
                        n3 / za * (zb - za));
      }
    }
  }
  cout << ans2 << endl;
}