Problem p02697 (C++) — buggy submission, verdict: Time Limit Exceeded

/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author zjsdut
 */

#ifndef ALGO_UTILS
#define ALGO_UTILS
#include <algorithm>
#include <cassert>
#include <queue>
#include <vector>
template <typename A, typename B> bool chkmin(A &a, const B &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}

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

using ll = long long;
using ull = unsigned long long;
using vl = std::vector<ll>;
using vb = std::vector<bool>;
using vi = std::vector<int>;
using pii = std::pair<int, int>;
using pli = std::pair<ll, int>;
using pil = std::pair<int, ll>;
using pll = std::pair<ll, ll>;
using vpii = std::vector<pii>;
template <typename T> using vv = std::vector<std::vector<T>>;
#define rng3(i, a, b)                                                          \\
  for (std::common_type<decltype(a), decltype(b)>::type i = a; i < b; ++i)
#define rng2(i, n) rng3(i, 0, n)
#define GET_MACRO(_1, _2, _3, NAME, ...) NAME
#define rng(...) GET_MACRO(__VA_ARGS__, rng3, rng2)(__VA_ARGS__)
#define up(i, a, b)                                                            \\
  for (std::common_type<decltype(a), decltype(b)>::type i = a; i <= b; ++i)
#define down(i, b, a)                                                          \\
  for (std::common_type<decltype(a), decltype(b)>::type i = b; i >= a; i--)
#define TOKENPASTE(x, y) x##y
#define TOKENPASTE2(x, y) TOKENPASTE(x, y)
#define rep(n)                                                                 \\
  for (int TOKENPASTE2(_iter_, __LINE__) = 0,                                  \\
                               TOKENPASTE2(_num_, __LINE__) = n;               \\
       TOKENPASTE2(_iter_, __LINE__) < TOKENPASTE2(_num_, __LINE__);           \\
       ++TOKENPASTE2(_iter_, __LINE__))
#define FOR(x, cont) for (const auto &x : cont)
#define For(x, cont) for (auto &x : cont)
#define ALL(x) begin(x), end(x)
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define ep emplace
#define SZ(x) (int)(x).size()
#define UNIQ(vec) (vec).erase(std::unique(all(vec)), std::end(vec))
#define LB(cont, x) int(std::lower_bound(all(cont), x) - std::begin(cont))
#define UB(cont, x) int(std::upper_bound(all(cont), x) - std::begin(cont))
template <typename T, typename U = std::less<T>>
using pq = std::priority_queue<T, std::vector<T>, U>;
template <typename T, typename U> T ceil(T x, U y) {
  assert(y > 0);
  if (x > 0)
    x += y - 1;
  return x / y;
}

template <typename T, typename U> T floor(T x, U y) {
  assert(y > 0);
  if (x < 0)
    x -= y - 1;
  return x / y;
}
#endif
#ifndef JHELPER_EXAMPLE_PROJECT_LIBRARY_IO_HPP_
#define JHELPER_EXAMPLE_PROJECT_LIBRARY_IO_HPP_
#include <iomanip>
#include <iostream>

struct fast_ios {
  fast_ios() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed << std::setprecision(10);
  };
} fast_ios_;

template <typename T>
std::istream &operator>>(std::istream &stream, std::vector<T> &vec) {
  for (auto &x : vec)
    stream >> x;
  return stream;
}

template <typename T, typename U>
std::istream &operator>>(std::istream &in, std::pair<T, U> &p) {
  in >> p.first >> p.second;
  return in;
}

void scan() {}

template <class T, class... Args> void scan(T &a, Args &...rest) {
  std::cin >> a;
  scan(rest...);
}

template <typename T>
std::ostream &operator<<(std::ostream &stream, const std::vector<T> &vec) {
  bool first = true;
  for (const T &t : vec) {
    if (first)
      first = false;
    else
      std::cout << ' ';
    std::cout << t;
  }
  return stream;
}

template <typename T, typename U>
std::ostream &operator<<(std::ostream &out, const std::pair<T, U> &p) {
  out << p.first << ' ' << p.second;
  return out;
}

template <typename T> void print(const std::vector<std::vector<T>> &t) {
  for (const auto &row : t) {
    std::cout << row << '\\n';
  }
}

template <typename T> void print(const T &t) { std::cout << t << ' '; }

template <typename T, typename... Args>
void print(const T &t, const Args &...rest) {
  print(t);
  print(rest...);
}

template <typename T> void println(const T &t) { std::cout << t << '\\n'; }

template <typename T, typename... Args>
void println(const T &t, const Args &...rest) {
  print(t);
  println(rest...);
}
#endif // JHELPER_EXAMPLE_PROJECT_LIBRARY_IO_HPP_

#include <bitset>
#include <set>

using std::to_string;
std::string to_string(const std::string &s) { return '"' + s + '"'; }

std::string to_string(const char *s) { return to_string((std::string)s); }

std::string to_string(bool b) { return (b ? "true" : "false"); }

template <typename A, typename B>
std::string to_string(const std::pair<A, B> &p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <size_t N> std::string to_string(const std::bitset<N> &bs) {
  return bs.to_string();
}
template <typename A> std::string to_string(const A &v) {
  bool first = true;
  std::string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

void debug_out() { std::cerr << std::endl; }

template <typename Head, typename... Tail>
void debug_out(const Head &H, const Tail &...T) {
  std::cerr << " " << to_string(H);
  debug_out(T...);
}

#if defined LOCAL
#define debug(...)                                                             \\
  std::cerr << "\\033[90m"                                                      \\
            << "[" << #__VA_ARGS__ << "]:",                                    \\
      debug_out(__VA_ARGS__), std::cerr << "\\033[0m"
#else
#define debug(...) 42
#endif

using namespace std;
class ERotationMatching {
public:
  static void solve(istream &, ostream &) {
    int n, m;
    scan(n, m);
    int odd = (m + 1) / 2;
    up(i, 1, odd) { println(i, odd * 2 + 1 - i); }
    int even = m / 2;
    int mid = even + 1 + odd * 2;
    up(i, 1, even) { println(mid - i, mid + i); }
  }
};
/*
 * Make sure that your laptop is plugged in or the build may be slow.
 */

#define in std::cin
#define out std::cout
int main() {
  ERotationMatching solver;
  solver.solve(in, out);
  return 0;
}


Error: TLE

Fixed submission:

/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author zjsdut
 */

#ifndef ALGO_UTILS
#define ALGO_UTILS
#include <algorithm>
#include <cassert>
#include <queue>
#include <vector>
template <typename A, typename B> bool chkmin(A &a, const B &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}

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

using ll = long long;
using ull = unsigned long long;
using vl = std::vector<ll>;
using vb = std::vector<bool>;
using vi = std::vector<int>;
using pii = std::pair<int, int>;
using pli = std::pair<ll, int>;
using pil = std::pair<int, ll>;
using pll = std::pair<ll, ll>;
using vpii = std::vector<pii>;
template <typename T> using vv = std::vector<std::vector<T>>;
#define rng3(i, a, b)                                                          \\
  for (std::common_type<decltype(a), decltype(b)>::type i = a; i < b; ++i)
#define rng2(i, n) rng3(i, 0, n)
#define GET_MACRO(_1, _2, _3, NAME, ...) NAME
#define rng(...) GET_MACRO(__VA_ARGS__, rng3, rng2)(__VA_ARGS__)
#define up(i, a, b)                                                            \\
  for (std::common_type<decltype(a), decltype(b)>::type i = a; i <= b; ++i)
#define down(i, b, a)                                                          \\
  for (std::common_type<decltype(a), decltype(b)>::type i = b; i >= a; i--)
#define TOKENPASTE(x, y) x##y
#define TOKENPASTE2(x, y) TOKENPASTE(x, y)
#define rep(n)                                                                 \\
  for (int TOKENPASTE2(_iter_, __LINE__) = 0,                                  \\
                               TOKENPASTE2(_num_, __LINE__) = n;               \\
       TOKENPASTE2(_iter_, __LINE__) < TOKENPASTE2(_num_, __LINE__);           \\
       ++TOKENPASTE2(_iter_, __LINE__))
#define FOR(x, cont) for (const auto &x : cont)
#define For(x, cont) for (auto &x : cont)
#define ALL(x) begin(x), end(x)
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define ep emplace
#define SZ(x) (int)(x).size()
#define UNIQ(vec) (vec).erase(std::unique(all(vec)), std::end(vec))
#define LB(cont, x) int(std::lower_bound(all(cont), x) - std::begin(cont))
#define UB(cont, x) int(std::upper_bound(all(cont), x) - std::begin(cont))
template <typename T, typename U = std::less<T>>
using pq = std::priority_queue<T, std::vector<T>, U>;
template <typename T, typename U> T ceil(T x, U y) {
  assert(y > 0);
  if (x > 0)
    x += y - 1;
  return x / y;
}

template <typename T, typename U> T floor(T x, U y) {
  assert(y > 0);
  if (x < 0)
    x -= y - 1;
  return x / y;
}
#endif
#ifndef JHELPER_EXAMPLE_PROJECT_LIBRARY_IO_HPP_
#define JHELPER_EXAMPLE_PROJECT_LIBRARY_IO_HPP_
#include <iomanip>
#include <iostream>

struct fast_ios {
  fast_ios() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed << std::setprecision(10);
  };
} fast_ios_;

template <typename T>
std::istream &operator>>(std::istream &stream, std::vector<T> &vec) {
  for (auto &x : vec)
    stream >> x;
  return stream;
}

template <typename T, typename U>
std::istream &operator>>(std::istream &in, std::pair<T, U> &p) {
  in >> p.first >> p.second;
  return in;
}

void scan() {}

template <class T, class... Args> void scan(T &a, Args &...rest) {
  std::cin >> a;
  scan(rest...);
}

template <typename T>
std::ostream &operator<<(std::ostream &stream, const std::vector<T> &vec) {
  bool first = true;
  for (const T &t : vec) {
    if (first)
      first = false;
    else
      std::cout << ' ';
    std::cout << t;
  }
  return stream;
}

template <typename T, typename U>
std::ostream &operator<<(std::ostream &out, const std::pair<T, U> &p) {
  out << p.first << ' ' << p.second;
  return out;
}

template <typename T> void print(const std::vector<std::vector<T>> &t) {
  for (const auto &row : t) {
    std::cout << row << '\\n';
  }
}

template <typename T> void print(const T &t) { std::cout << t << ' '; }

template <typename T, typename... Args>
void print(const T &t, const Args &...rest) {
  print(t);
  print(rest...);
}

template <typename T> void println(const T &t) { std::cout << t << '\\n'; }

template <typename T, typename... Args>
void println(const T &t, const Args &...rest) {
  print(t);
  println(rest...);
}
#endif // JHELPER_EXAMPLE_PROJECT_LIBRARY_IO_HPP_

using namespace std;
class ERotationMatching {
public:
  static void solve(istream &, ostream &) {
    int n, m;
    scan(n, m);
    vb used(n);
    int j = 0;
    up(i, 1, m) {
      while (used[j % n] || used[(j + i) % n])
        ++j;
      println(j % n + 1, (j + i) % n + 1);
      used[j % n] = used[(j + i) % n] = true;
    }
  }
};
/*
 * Make sure that your laptop is plugged in or the build may be slow.
 */

#define in std::cin
#define out std::cout
int main() {
  ERotationMatching solver;
  solver.solve(in, out);
  return 0;
}