Problem p02560 (C++) — buggy submission, verdict: Runtime Error

///////////////////////////////////////////////////////////////////////////////

#include <bits/stdc++.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>

using namespace std;

///////////////////////////////////////////////////////////////////////////////

#define DEBUG 0

#define pb push_back
#define V vector
#define M unordered_map
#define S static

#define rep(i, n) for (ll i = 0LL; i < n; ++i)
#define srep(i, s, n) for (ll i = s; i < n; ++i)
#define rrep(i, n) for (ll i = n - 1LL; i >= 0LL; --i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define CIN(x)                                                                 \\
  do {                                                                         \\
    assert(!cin.eof());                                                        \\
    cin >> x;                                                                  \\
    assert(!cin.fail());                                                       \\
  } while (0);
#if DEBUG
#define debug_print(...) _debug_print(__VA_ARGS__)
#define debug_printf(...) printf(__VA_ARGS__)
#define debug_print_time _debug_print_time
#else // DEBUG
#define debug_print(...)
#define debug_printf(...)
#define debug_print_time
#endif // DEBUG

typedef long long ll;
typedef unsigned long long ull;
typedef tuple<ll, ll> t2;
typedef tuple<ll, ll, ll> t3;
typedef tuple<ll, ll, ll, ll> t4;
typedef tuple<ll, ll, ll, ll, ll> t5;
template <typename T>
using priority_queue_incr = priority_queue<T, V<T>, greater<T>>;

///////////////////////////////////////////////////////////////////////////////

template <typename TT, typename T> T get_m(M<TT, T> &m, TT k, T default_value) {
  if (m.find(k) == m.end())
    return m[k] = default_value;
  return m[k];
}

template <typename TT, typename T> void incr_m(M<TT, T> &m, TT k) {
  if (m.find(k) == m.end())
    m[k] = 0;
  m[k]++;
}

template <typename TT, typename T> void incr_m(map<TT, T> &m, TT k) {
  if (m.find(k) == m.end())
    m[k] = 0;
  m[k]++;
}

void llin(ll &a) { CIN(a); }

void llinl1(V<ll> &v, ll count) {
  for (ll i = 0LL; i < count; ++i) {
    ll a;
    CIN(a);
    v.push_back(a);
  }
}

void llinl2(V<t2> &v, ll count) {
  for (ll i = 0LL; i < count; ++i) {
    ll a, b;
    CIN(a >> b);
    v.push_back(t2(a, b));
  }
}

void llinl3(V<t3> &v, ll count) {
  for (ll i = 0LL; i < count; ++i) {
    ll a, b, c;
    CIN(a >> b >> c);
    v.push_back(t3(a, b, c));
  }
}

void llinl4(V<t4> &v, ll count) {
  for (ll i = 0LL; i < count; ++i) {
    ll a, b, c, d;
    CIN(a >> b >> c >> d);
    v.push_back(t4(a, b, c, d));
  }
}

void llina(V<ll> &v, ll count) { llinl1(v, count); }

template <typename T> void sort(V<T> &v) { sort(v.begin(), v.end()); }

template <typename T> void sort_reverse(V<T> &v) {
  sort(v.begin(), v.end(), greater<T>());
}

template <typename T> void _debug_print(T x) { cout << x << endl; }

void _debug_print(const t2 &x) {
  ll x1 = get<0>(x);
  ll x2 = get<1>(x);
  cout << "-- " << x1 << " -- " << x2 << endl;
}

void _debug_print(const t3 &x) {
  ll x1 = get<0>(x);
  ll x2 = get<1>(x);
  ll x3 = get<2>(x);
  cout << "-- " << x1 << " -- " << x2 << " -- " << x3 << endl;
}

void _debug_print(const t4 &x) {
  ll x1 = get<0>(x);
  ll x2 = get<1>(x);
  ll x3 = get<2>(x);
  ll x4 = get<3>(x);
  cout << "-- " << x1 << " -- " << x2 << " -- " << x3 << " -- " << x4 << endl;
}

template <typename T> void _debug_print(T xarray[], ll n) {
  rep(i, n) _debug_print(xarray[i]);
}

template <typename T> void _debug_print(const V<T> &xlist) {
  for (auto x : xlist) {
    cout << "-- ";
    _debug_print(x);
  }
}

template <typename T> void _debug_print(const set<T> &xset) {
  for (auto x : xset) {
    cout << "-- ";
    _debug_print(x);
  }
}

template <typename TT, typename T> void _debug_print(const M<TT, T> &xlist) {
  for (auto x : xlist) {
    TT k = x.first;
    T v = x.second;
    cout << "====" << endl;
    cout << "K=";
    _debug_print(k);
    cout << "V=";
    _debug_print(v);
  }
}

template <typename TT, typename T> void _debug_print(const map<TT, T> &xlist) {
  for (auto x : xlist) {
    TT k = x.first;
    T v = x.second;
    cout << "====" << endl;
    cout << "K=";
    _debug_print(k);
    cout << "V=";
    _debug_print(v);
  }
}

void _debug_print_time(const char *prefix) {
  struct timeval tv;
  gettimeofday(&tv, NULL);
#if DEBUG
  struct tm *tm = localtime(&tv.tv_sec);
#endif
  debug_printf("-- %s %02d:%02d:%02d.%06ld\\n", prefix, tm->tm_hour, tm->tm_min,
               tm->tm_sec, tv.tv_usec);
}

///////////////////////////////////////////////////////////////////////////////

void _main();
int main() {
  cout << setprecision(12);
#if !DEBUG
  ios::sync_with_stdio(false);
  cin.tie(0);
#endif

  _main();
  return 0;
}

ll floor_sum(ll n, ll m, ll a, ll b) {
  ll aq = a / m;
  a = a % m;

  ll bq = b / m;
  b = b % m;

  ll y = (n * a + b) / m;
  ll x = m * y - b;

  ll ret = 0;
  ret += n * (n - 1LL) * aq / 2LL;
  ret += n * bq;

  if (!y)
    return ret;
  if (!a)
    return ret + (b / m) * n;

  ret += (n - (x / a + !!(x % a))) * y;
  ret += floor_sum(y, a, m, (a - x % a) % a);
  return ret;
}

void solve() {
  ll n;
  llin(n);
  ll m;
  llin(m);
  ll a;
  llin(a);
  ll b;
  llin(b);

  cout << floor_sum(n, m, a, b) << endl;
}

void _main() {
  ll t;
  llin(t);
  rep(i, t) solve();
}

///////////////////////////////////////////////////////////////////////////////


Error: 0

Fixed submission:

///////////////////////////////////////////////////////////////////////////////

#include <bits/stdc++.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>

using namespace std;

///////////////////////////////////////////////////////////////////////////////

#define DEBUG 0

#define pb push_back
#define V vector
#define M unordered_map
#define S static

#define rep(i, n) for (ll i = 0LL; i < n; ++i)
#define srep(i, s, n) for (ll i = s; i < n; ++i)
#define rrep(i, n) for (ll i = n - 1LL; i >= 0LL; --i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define CIN(x)                                                                 \\
  do {                                                                         \\
    assert(!cin.eof());                                                        \\
    cin >> x;                                                                  \\
    assert(!cin.fail());                                                       \\
  } while (0);
#if DEBUG
#define debug_print(...) _debug_print(__VA_ARGS__)
#define debug_printf(...) printf(__VA_ARGS__)
#define debug_print_time _debug_print_time
#else // DEBUG
#define debug_print(...)
#define debug_printf(...)
#define debug_print_time
#endif // DEBUG

typedef long long ll;
typedef unsigned long long ull;
typedef tuple<ll, ll> t2;
typedef tuple<ll, ll, ll> t3;
typedef tuple<ll, ll, ll, ll> t4;
typedef tuple<ll, ll, ll, ll, ll> t5;
template <typename T>
using priority_queue_incr = priority_queue<T, V<T>, greater<T>>;

///////////////////////////////////////////////////////////////////////////////

template <typename TT, typename T> T get_m(M<TT, T> &m, TT k, T default_value) {
  if (m.find(k) == m.end())
    return m[k] = default_value;
  return m[k];
}

template <typename TT, typename T> void incr_m(M<TT, T> &m, TT k) {
  if (m.find(k) == m.end())
    m[k] = 0;
  m[k]++;
}

template <typename TT, typename T> void incr_m(map<TT, T> &m, TT k) {
  if (m.find(k) == m.end())
    m[k] = 0;
  m[k]++;
}

void llin(ll &a) { CIN(a); }

void llinl1(V<ll> &v, ll count) {
  for (ll i = 0LL; i < count; ++i) {
    ll a;
    CIN(a);
    v.push_back(a);
  }
}

void llinl2(V<t2> &v, ll count) {
  for (ll i = 0LL; i < count; ++i) {
    ll a, b;
    CIN(a >> b);
    v.push_back(t2(a, b));
  }
}

void llinl3(V<t3> &v, ll count) {
  for (ll i = 0LL; i < count; ++i) {
    ll a, b, c;
    CIN(a >> b >> c);
    v.push_back(t3(a, b, c));
  }
}

void llinl4(V<t4> &v, ll count) {
  for (ll i = 0LL; i < count; ++i) {
    ll a, b, c, d;
    CIN(a >> b >> c >> d);
    v.push_back(t4(a, b, c, d));
  }
}

void llina(V<ll> &v, ll count) { llinl1(v, count); }

template <typename T> void sort(V<T> &v) { sort(v.begin(), v.end()); }

template <typename T> void sort_reverse(V<T> &v) {
  sort(v.begin(), v.end(), greater<T>());
}

template <typename T> void _debug_print(T x) { cout << x << endl; }

void _debug_print(const t2 &x) {
  ll x1 = get<0>(x);
  ll x2 = get<1>(x);
  cout << "-- " << x1 << " -- " << x2 << endl;
}

void _debug_print(const t3 &x) {
  ll x1 = get<0>(x);
  ll x2 = get<1>(x);
  ll x3 = get<2>(x);
  cout << "-- " << x1 << " -- " << x2 << " -- " << x3 << endl;
}

void _debug_print(const t4 &x) {
  ll x1 = get<0>(x);
  ll x2 = get<1>(x);
  ll x3 = get<2>(x);
  ll x4 = get<3>(x);
  cout << "-- " << x1 << " -- " << x2 << " -- " << x3 << " -- " << x4 << endl;
}

template <typename T> void _debug_print(T xarray[], ll n) {
  rep(i, n) _debug_print(xarray[i]);
}

template <typename T> void _debug_print(const V<T> &xlist) {
  for (auto x : xlist) {
    cout << "-- ";
    _debug_print(x);
  }
}

template <typename T> void _debug_print(const set<T> &xset) {
  for (auto x : xset) {
    cout << "-- ";
    _debug_print(x);
  }
}

template <typename TT, typename T> void _debug_print(const M<TT, T> &xlist) {
  for (auto x : xlist) {
    TT k = x.first;
    T v = x.second;
    cout << "====" << endl;
    cout << "K=";
    _debug_print(k);
    cout << "V=";
    _debug_print(v);
  }
}

template <typename TT, typename T> void _debug_print(const map<TT, T> &xlist) {
  for (auto x : xlist) {
    TT k = x.first;
    T v = x.second;
    cout << "====" << endl;
    cout << "K=";
    _debug_print(k);
    cout << "V=";
    _debug_print(v);
  }
}

void _debug_print_time(const char *prefix) {
  struct timeval tv;
  gettimeofday(&tv, NULL);
#if DEBUG
  struct tm *tm = localtime(&tv.tv_sec);
#endif
  debug_printf("-- %s %02d:%02d:%02d.%06ld\\n", prefix, tm->tm_hour, tm->tm_min,
               tm->tm_sec, tv.tv_usec);
}

///////////////////////////////////////////////////////////////////////////////

void _main();
int main() {
  cout << setprecision(12);
#if !DEBUG
  ios::sync_with_stdio(false);
  cin.tie(0);
#endif

  _main();
  return 0;
}

ll floor_sum(ll n, ll m, ll a, ll b) {
  if (!n)
    return 0;
  if (n == 1)
    return b / m;
  if (!a)
    return (b / m) * n;
  assert(m);

  ll aq = a / m;
  a = a % m;

  ll bq = b / m;
  b = b % m;

  ll y = (n * a + b) / m;
  ll x = m * y - b;

  ll ret = 0;
  ret += n * (n - 1LL) * aq / 2LL;
  ret += n * bq;
  ret += (n - (x / a + !!(x % a))) * y;
  ret += floor_sum(y, a, m, (a - x % a) % a);
  return ret;
}

void solve() {
  ll n;
  llin(n);
  ll m;
  llin(m);
  ll a;
  llin(a);
  ll b;
  llin(b);

  cout << floor_sum(n, m, a, b) << endl;
}

void _main() {
  ll t;
  llin(t);
  rep(i, t) solve();
}

///////////////////////////////////////////////////////////////////////////////