Problem p02697 (C++) — buggy submission, verdict: Runtime Error

#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define repd(i, a, b) for (int i = (a); i < (b); i++)
#define rep(i, n) repd(i, 0, n)
using ll = long long;
using ld = long double;
#define int ll
#define double ld
#define VARNAME(v) #v
using P = pair<int, int>;
constexpr int MOD = 1000000007;
// constexpr  int MOD = 998244353;
constexpr ll INF = 1e16;
#pragma region tmp
constexpr double EPS = 1e-10;
constexpr double PI = 3.141592653589793;
const string endn = "\\n";
const string abc = "abcdefghijklmnopqrstuvwxyz";
const string ABC = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
template <class T1, class T2>
ostream &operator<<(ostream &out, const pair<T1, T2> &o) {
  out << "(" << o.first << ", " << o.second << ")";
  return out;
}
template <class T> ostream &operator<<(ostream &out, const vector<T> &o) {
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (itr + 1 != o.end() ? " " : "");
  return out;
}
template <class T> ostream &operator<<(ostream &out, const deque<T> &o) {
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (itr + 1 != o.end() ? " " : "");
  return out;
}
template <class T> ostream &operator<<(ostream &out, const set<T> &o) {
  out << "{";
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (next(itr, 1) != o.end() ? "," : "");
  out << "}";
  return out;
}
template <class T> ostream &operator<<(ostream &out, const multiset<T> &o) {
  out << "{";
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (next(itr, 1) != o.end() ? "," : "");
  out << "}";
  return out;
}
template <class T, class U>
ostream &operator<<(ostream &out, const map<T, U> &o) {
  out << "{";
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (next(itr, 1) != o.end() ? " " : "");
  out << "}";
  return out;
}
template <class T, class U>
ostream &operator<<(ostream &out, const multimap<T, U> &o) {
  out << "{";
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (next(itr, 1) != o.end() ? " " : "");
  out << "}";
  return out;
}
template <class T> ostream &operator<<(ostream &out, queue<T> o) {
  while (!o.empty())
    out << o.front() << (o.size() > 0 ? " " : ""), o.pop();
  return out;
}
template <class T, class U>
ostream &operator<<(ostream &out, priority_queue<T, vector<T>, U> o) {
  while (!o.empty())
    out << o.top() << (o.size() > 0 ? " " : ""), o.pop();
  return out;
}
template <class T> ostream &operator<<(ostream &out, stack<T> o) {
  while (!o.empty())
    out << o.top() << (o.size() > 0 ? " " : ""), o.pop();
  return out;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, initializer_list<T> b) {
  T c = min(b);
  if (a > c) {
    a = c;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmax(T &a, initializer_list<T> b) {
  T c = max(b);
  if (a < c) {
    a = c;
    return 1;
  }
  return 0;
}
inline int mrep(int &a, int M = MOD) {
  a %= M;
  return a = (a < 0 ? a + M : a);
}
inline int add(int &a, int b, int M = MOD) {
  return a = (mrep(a, M) + mrep(b, M)) % M;
}
inline int mul(int &a, int b, int M = MOD) {
  return a = (mrep(a, M) * mrep(b, M)) % M;
}
inline int add(int &a, initializer_list<int> b, int M = MOD) {
  return a = (mrep(a, M) + accumulate(b.begin(), b.end(), (int)0,
                                      [&M](int acc, int i) {
                                        return (acc + mrep(i, M)) % M;
                                      })) %
             M;
}
inline int mul(int &a, initializer_list<int> b, int M = MOD) {
  return a = (mrep(a, M) * accumulate(b.begin(), b.end(), (int)1,
                                      [&M](int acc, int i) {
                                        return (acc * mrep(i, M)) % M;
                                      })) %
             M;
}
inline int modpow(int b, int e, int M = MOD) {
  int ret = 1;
  while (e > 0) {
    if (e % 2)
      mul(ret, b, M);
    mul(b, b, M);
    e /= 2;
  };
  return ret;
}
inline int modinv(int a, int M = MOD) {
  int b = M, u = 1, v = 0;
  while (b) {
    int t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  return mrep(u, M);
}
template <class T> inline void print(T a) { cout << a << endl; }
template <class T> inline void print(vector<T> a, int n) {
  chmin(n, int(a.size()));
  rep(i, n) cout << a[i] << (i != n - 1 ? " " : "\\n");
}
template <class T, size_t SIZE> inline void print(T (&a)[SIZE], int n = SIZE) {
  chmin(n, int(SIZE));
  rep(i, n) cout << a[i] << (i != n - 1 ? " " : "\\n");
}
#pragma #endregion tmp

int n, k, q, a[2100];
P ind[2100];
int bit[2100];
void badd(int i, int x) {
  while (i <= n) {
    bit[i] += x;
    i += (i & -i);
  }
}
int sum(int i) {
  int ret = 0;
  while (i > 0) {
    ret += bit[i];
    i -= (i & -i);
  }
  return ret;
}
signed main() {
  int n, m;
  cin >> n >> m;
  vector<P> ans;
  int s = 0, d = 1;
  rep(i, m - m / 2) {
    ans.push_back(P(s, (s - d + n) % n));
    s++;
    d += 2;
  }
  s = m + 1;
  d = 2;
  rep(i, m / 2) {
    ans.push_back(P(s, (s - d + n) % n));
    s++;
    d += 2;
  }
  rep(i, m) cout << ans[i].first + 1 << " " << ans[i].second + 1 << endl;
}


Error: -6
a85048fe-4f5d-40e3-826e-0e64d6c4b559.out: /home/alex/Documents/bug-detection/input/Project_CodeNet/data/p02697/C++/s262184980.cpp:68: int main(): Assertion `n%2' failed.


Fixed submission:

#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define repd(i, a, b) for (int i = (a); i < (b); i++)
#define rep(i, n) repd(i, 0, n)
using ll = long long;
using ld = long double;
#define int ll
#define double ld
#define VARNAME(v) #v
using P = pair<int, int>;
constexpr int MOD = 1000000007;
// constexpr  int MOD = 998244353;
constexpr ll INF = 1e16;
#pragma region tmp
constexpr double EPS = 1e-10;
constexpr double PI = 3.141592653589793;
const string endn = "\\n";
const string abc = "abcdefghijklmnopqrstuvwxyz";
const string ABC = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
template <class T1, class T2>
ostream &operator<<(ostream &out, const pair<T1, T2> &o) {
  out << "(" << o.first << ", " << o.second << ")";
  return out;
}
template <class T> ostream &operator<<(ostream &out, const vector<T> &o) {
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (itr + 1 != o.end() ? " " : "");
  return out;
}
template <class T> ostream &operator<<(ostream &out, const deque<T> &o) {
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (itr + 1 != o.end() ? " " : "");
  return out;
}
template <class T> ostream &operator<<(ostream &out, const set<T> &o) {
  out << "{";
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (next(itr, 1) != o.end() ? "," : "");
  out << "}";
  return out;
}
template <class T> ostream &operator<<(ostream &out, const multiset<T> &o) {
  out << "{";
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (next(itr, 1) != o.end() ? "," : "");
  out << "}";
  return out;
}
template <class T, class U>
ostream &operator<<(ostream &out, const map<T, U> &o) {
  out << "{";
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (next(itr, 1) != o.end() ? " " : "");
  out << "}";
  return out;
}
template <class T, class U>
ostream &operator<<(ostream &out, const multimap<T, U> &o) {
  out << "{";
  for (auto itr = o.begin(); itr != o.end(); itr++)
    out << *itr << (next(itr, 1) != o.end() ? " " : "");
  out << "}";
  return out;
}
template <class T> ostream &operator<<(ostream &out, queue<T> o) {
  while (!o.empty())
    out << o.front() << (o.size() > 0 ? " " : ""), o.pop();
  return out;
}
template <class T, class U>
ostream &operator<<(ostream &out, priority_queue<T, vector<T>, U> o) {
  while (!o.empty())
    out << o.top() << (o.size() > 0 ? " " : ""), o.pop();
  return out;
}
template <class T> ostream &operator<<(ostream &out, stack<T> o) {
  while (!o.empty())
    out << o.top() << (o.size() > 0 ? " " : ""), o.pop();
  return out;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, initializer_list<T> b) {
  T c = min(b);
  if (a > c) {
    a = c;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmax(T &a, initializer_list<T> b) {
  T c = max(b);
  if (a < c) {
    a = c;
    return 1;
  }
  return 0;
}
inline int mrep(int &a, int M = MOD) {
  a %= M;
  return a = (a < 0 ? a + M : a);
}
inline int add(int &a, int b, int M = MOD) {
  return a = (mrep(a, M) + mrep(b, M)) % M;
}
inline int mul(int &a, int b, int M = MOD) {
  return a = (mrep(a, M) * mrep(b, M)) % M;
}
inline int add(int &a, initializer_list<int> b, int M = MOD) {
  return a = (mrep(a, M) + accumulate(b.begin(), b.end(), (int)0,
                                      [&M](int acc, int i) {
                                        return (acc + mrep(i, M)) % M;
                                      })) %
             M;
}
inline int mul(int &a, initializer_list<int> b, int M = MOD) {
  return a = (mrep(a, M) * accumulate(b.begin(), b.end(), (int)1,
                                      [&M](int acc, int i) {
                                        return (acc * mrep(i, M)) % M;
                                      })) %
             M;
}
inline int modpow(int b, int e, int M = MOD) {
  int ret = 1;
  while (e > 0) {
    if (e % 2)
      mul(ret, b, M);
    mul(b, b, M);
    e /= 2;
  };
  return ret;
}
inline int modinv(int a, int M = MOD) {
  int b = M, u = 1, v = 0;
  while (b) {
    int t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  return mrep(u, M);
}
template <class T> inline void print(T a) { cout << a << endl; }
template <class T> inline void print(vector<T> a, int n) {
  chmin(n, int(a.size()));
  rep(i, n) cout << a[i] << (i != n - 1 ? " " : "\\n");
}
template <class T, size_t SIZE> inline void print(T (&a)[SIZE], int n = SIZE) {
  chmin(n, int(SIZE));
  rep(i, n) cout << a[i] << (i != n - 1 ? " " : "\\n");
}
#pragma #endregion tmp

int n, k, q, a[2100];
P ind[2100];
int bit[2100];
void badd(int i, int x) {
  while (i <= n) {
    bit[i] += x;
    i += (i & -i);
  }
}
int sum(int i) {
  int ret = 0;
  while (i > 0) {
    ret += bit[i];
    i -= (i & -i);
  }
  return ret;
}
signed main() {
  int n, m;
  cin >> n >> m;
  vector<P> ans;
  int s = 0, d = 1;
  assert(n % 2);
  rep(i, m) {
    ans.push_back(P(s, (s + d) % n));
    add(s, -1, n);
    d += 2;
  }
  rep(i, m) cout << ans[i].first + 1 << " " << ans[i].second + 1 << endl;
}