Problem p03466 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define MP make_pair
#define PB push_back
#define int long long
#define st first
#define nd second
#define rd third
#define FOR(i, a, b) for (int i = (a); i <= (b); ++i)
#define RE(i, n) FOR(i, 1, n)
#define FORD(i, a, b) for (int i = (a); i >= (b); --i)
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define VAR(v, i) __typeof(i) v = (i)
#define FORE(i, c) for (VAR(i, (c).begin()); i != (c).end(); ++i)
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
using namespace std;
template <typename TH> void _dbg(const char *sdbg, TH h) {
  cerr << sdbg << "=" << h << "\n";
}
template <typename TH, typename... TA>
void _dbg(const char *sdbg, TH h, TA... t) {
  while (*sdbg != ',')
    cerr << *sdbg++;
  cerr << "=" << h << ",";
  _dbg(sdbg + 1, t...);
}
#ifdef LOCAL
#define debug(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define debugv(x)                                                              \
  {                                                                            \
    {                                                                          \
      cerr << #x << " = ";                                                     \
      FORE(itt, (x)) cerr << *itt << ", ";                                     \
      cerr << "\n";                                                            \
    }                                                                          \
  }
#else
#define debug(...) (__VA_ARGS__)
#define debugv(x)
#define cerr                                                                   \
  if (0)                                                                       \
  cout
#endif
#define next ____next
#define prev ____prev
#define left ____left
#define hash ____hash
typedef long long ll;
typedef long double LD;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VLL;
typedef vector<pair<int, int>> VPII;
typedef vector<pair<ll, ll>> VPLL;

template <class C> void mini(C &a4, C b4) { a4 = min(a4, b4); }
template <class C> void maxi(C &a4, C b4) { a4 = max(a4, b4); }
template <class T1, class T2>
ostream &operator<<(ostream &out, pair<T1, T2> pair) {
  return out << "(" << pair.first << ", " << pair.second << ")";
}
template <class A, class B, class C> struct Triple {
  A first;
  B second;
  C third;
  bool operator<(const Triple &t) const {
    if (st != t.st)
      return st < t.st;
    if (nd != t.nd)
      return nd < t.nd;
    return rd < t.rd;
  }
};
template <class T> void ResizeVec(T &, vector<int>) {}
template <class T> void ResizeVec(vector<T> &vec, vector<int> sz) {
  vec.resize(sz[0]);
  sz.erase(sz.begin());
  if (sz.empty()) {
    return;
  }
  for (T &v : vec) {
    ResizeVec(v, sz);
  }
}
typedef Triple<int, int, int> TIII;
template <class A, class B, class C>
ostream &operator<<(ostream &out, Triple<A, B, C> t) {
  return out << "(" << t.st << ", " << t.nd << ", " << t.rd << ")";
}
template <class T> ostream &operator<<(ostream &out, vector<T> vec) {
  out << "(";
  for (auto &v : vec)
    out << v << ", ";
  return out << ")";
}
template <class T> ostream &operator<<(ostream &out, set<T> vec) {
  out << "(";
  for (auto &v : vec)
    out << v << ", ";
  return out << ")";
}

int32_t main() {

  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(10);
  cerr << fixed << setprecision(10);
  cin.tie(0);
  // double beg_clock = 1.0 * clock() / CLOCKS_PER_SEC;

  int q;
  cin >> q;
  RE(_, q) {
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    int sw = 0;
    int n = a + b;
    if (a >= b) {
    } else {
      sw = 1;
      c = n - c + 1;
      d = n - d + 1;
      swap(a, b);
      swap(c, d);
    }
    int gr = (a + b) / (b + 1);
    int pref = 1, kl = 1, kp = n;
    while (kl <= kp) {
      int aktc = (kl + kp) / 2;
      int full_gr = aktc / (gr + 1);
      int rem_b = b - full_gr;
      int rem_a = a - (aktc - full_gr);
      if (aktc % (full_gr) == 0) {
        rem_b++;
      }
      if (rem_a >= 0 && rem_b <= (rem_a + 1) * gr) {
        pref = aktc;
        kl = aktc + 1;
      } else {
        kp = aktc - 1;
      }
    }
    int x = pref / (gr + 1);
    int y = pref - x * (gr + 1);
    // int rem_b = b - x;
    int t = a - (gr * x + y);
    int z = b - x - gr * t;
    debug(a, b, gr, pref, x, y, z, t);
    assert(gr * x + y + t == a);
    assert(x + z + gr * t == b);
    string res;
    debug(a, b, c, d, gr);
    //     string res;
    FOR(i, c, d) {
      if (i <= pref) {
        if (i % (gr + 1) == 0) {
          res += 'B';
        } else {
          res += 'A';
        }
      } else if (i <= pref + z) {
        res += 'B';
      } else if ((n + 1 - i) % (gr + 1) == 0) {
        res += 'A';
      } else {
        res += 'B';
      }
    }
    if (sw == 0) {
      cout << res << "\n";
    } else {
      reverse(ALL(res));
      for (auto &cc : res) {
        cc = 'A' + 'B' - cc;
      }
      cout << res << "\n";
    }
  }

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#define MP make_pair
#define PB push_back
#define int long long
#define st first
#define nd second
#define rd third
#define FOR(i, a, b) for (int i = (a); i <= (b); ++i)
#define RE(i, n) FOR(i, 1, n)
#define FORD(i, a, b) for (int i = (a); i >= (b); --i)
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define VAR(v, i) __typeof(i) v = (i)
#define FORE(i, c) for (VAR(i, (c).begin()); i != (c).end(); ++i)
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
using namespace std;
template <typename TH> void _dbg(const char *sdbg, TH h) {
  cerr << sdbg << "=" << h << "\n";
}
template <typename TH, typename... TA>
void _dbg(const char *sdbg, TH h, TA... t) {
  while (*sdbg != ',')
    cerr << *sdbg++;
  cerr << "=" << h << ",";
  _dbg(sdbg + 1, t...);
}
#ifdef LOCAL
#define debug(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define debugv(x)                                                              \
  {                                                                            \
    {                                                                          \
      cerr << #x << " = ";                                                     \
      FORE(itt, (x)) cerr << *itt << ", ";                                     \
      cerr << "\n";                                                            \
    }                                                                          \
  }
#else
#define debug(...) (__VA_ARGS__)
#define debugv(x)
#define cerr                                                                   \
  if (0)                                                                       \
  cout
#endif
#define next ____next
#define prev ____prev
#define left ____left
#define hash ____hash
typedef long long ll;
typedef long double LD;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VLL;
typedef vector<pair<int, int>> VPII;
typedef vector<pair<ll, ll>> VPLL;

template <class C> void mini(C &a4, C b4) { a4 = min(a4, b4); }
template <class C> void maxi(C &a4, C b4) { a4 = max(a4, b4); }
template <class T1, class T2>
ostream &operator<<(ostream &out, pair<T1, T2> pair) {
  return out << "(" << pair.first << ", " << pair.second << ")";
}
template <class A, class B, class C> struct Triple {
  A first;
  B second;
  C third;
  bool operator<(const Triple &t) const {
    if (st != t.st)
      return st < t.st;
    if (nd != t.nd)
      return nd < t.nd;
    return rd < t.rd;
  }
};
template <class T> void ResizeVec(T &, vector<int>) {}
template <class T> void ResizeVec(vector<T> &vec, vector<int> sz) {
  vec.resize(sz[0]);
  sz.erase(sz.begin());
  if (sz.empty()) {
    return;
  }
  for (T &v : vec) {
    ResizeVec(v, sz);
  }
}
typedef Triple<int, int, int> TIII;
template <class A, class B, class C>
ostream &operator<<(ostream &out, Triple<A, B, C> t) {
  return out << "(" << t.st << ", " << t.nd << ", " << t.rd << ")";
}
template <class T> ostream &operator<<(ostream &out, vector<T> vec) {
  out << "(";
  for (auto &v : vec)
    out << v << ", ";
  return out << ")";
}
template <class T> ostream &operator<<(ostream &out, set<T> vec) {
  out << "(";
  for (auto &v : vec)
    out << v << ", ";
  return out << ")";
}

int32_t main() {

  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(10);
  cerr << fixed << setprecision(10);
  cin.tie(0);
  // double beg_clock = 1.0 * clock() / CLOCKS_PER_SEC;

  int q;
  cin >> q;
  RE(_, q) {
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    int sw = 0;
    int n = a + b;
    if (a >= b) {
    } else {
      sw = 1;
      c = n - c + 1;
      d = n - d + 1;
      swap(a, b);
      swap(c, d);
    }
    int gr = (a + b) / (b + 1);
    int pref = 1, kl = 1, kp = n;
    while (kl <= kp) {
      int aktc = (kl + kp) / 2;
      int full_gr = aktc / (gr + 1);
      int rem_b = b - full_gr;
      int rem_a = a - (aktc - full_gr);
      if (aktc % (gr + 1) == 0) {
        rem_b++;
      }
      if (rem_a >= 0 && rem_b <= (rem_a + 1) * gr) {
        pref = aktc;
        kl = aktc + 1;
      } else {
        kp = aktc - 1;
      }
    }
    int x = pref / (gr + 1);
    int y = pref - x * (gr + 1);
    // int rem_b = b - x;
    int t = a - (gr * x + y);
    int z = b - x - gr * t;
    debug(a, b, gr, pref, x, y, z, t);
    assert(gr * x + y + t == a);
    assert(x + z + gr * t == b);
    string res;
    debug(a, b, c, d, gr);
    //     string res;
    FOR(i, c, d) {
      if (i <= pref) {
        if (i % (gr + 1) == 0) {
          res += 'B';
        } else {
          res += 'A';
        }
      } else if (i <= pref + z) {
        res += 'B';
      } else if ((n + 1 - i) % (gr + 1) == 0) {
        res += 'A';
      } else {
        res += 'B';
      }
    }
    if (sw == 0) {
      cout << res << "\n";
    } else {
      reverse(ALL(res));
      for (auto &cc : res) {
        cc = 'A' + 'B' - cc;
      }
      cout << res << "\n";
    }
  }

  return 0;
}