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

// #define _GLIBCXX_DEBUG
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pdd = pair<double, double>;
using pss = pair<string, string>;
using pcc = pair<char, char>;
using pbb = pair<bool, bool>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using ti3 = tuple<int, int, int>;
using tl3 = tuple<ll, ll, ll>;
using td3 = tuple<double, double, double>;
using ts3 = tuple<string, string, string>;
using tc3 = tuple<char, char, char>;
using tb3 = tuple<bool, bool, bool>;
using ti4 = tuple<int, int, int, int>;
using tl4 = tuple<ll, ll, ll, ll>;
using td4 = tuple<double, double, double, double>;
using ts4 = tuple<string, string, string, string>;
using tc4 = tuple<char, char, char, char>;
using tb4 = tuple<bool, bool, bool, bool>;
using vi = vector<int>;
using vl = vector<ll>;
using vd = vector<double>;
using vs = vector<string>;
using vc = vector<char>;
using vb = vector<bool>;
using vvi = vector<vi>;
using vvl = vector<vl>;
using vvd = vector<vd>;
using vvs = vector<vs>;
using vvc = vector<vc>;
using vvb = vector<vb>;
using vvvi = vector<vvi>;
using vvvl = vector<vvl>;
using vvvd = vector<vvd>;
using vvvs = vector<vvs>;
using vvvc = vector<vvc>;
using vvvb = vector<vvb>;
using vpii = vector<pii>;
using vpll = vector<pll>;
using vpdd = vector<pdd>;
using vpss = vector<pss>;
using vpcc = vector<pcc>;
using vpbb = vector<pbb>;
using vpil = vector<pil>;
using vpli = vector<pli>;
using vti3 = vector<ti3>;
using vtl3 = vector<tl3>;
using vtd3 = vector<td3>;
using vts3 = vector<ts3>;
using vtc3 = vector<tc3>;
using vtb3 = vector<tb3>;
using vti4 = vector<ti4>;
using vtl4 = vector<tl4>;
using vtd4 = vector<td4>;
using vts4 = vector<ts4>;
using vtc4 = vector<tc4>;
using vtb4 = vector<tb4>;
using mii = map<int, int>;
using mll = map<ll, ll>;
using msi = map<string, int>;
using mci = map<char, int>;
using mil = map<int, ll>;
using mli = map<ll, int>;
using si = set<int>;
using sl = set<ll>;
using sd = set<double>;
using ss = set<string>;
using sc = set<char>;
using sb = set<bool>;
using spii = set<pii>;
using spll = set<pll>;
using spdd = set<pdd>;
using spss = set<pss>;
using spcc = set<pcc>;
using spbb = set<pbb>;
using spil = set<pil>;
using spli = set<pli>;
using sti3 = set<ti3>;
using stl3 = set<tl3>;
using std3 = set<td3>;
using sts3 = set<ts3>;
using stc3 = set<tc3>;
using stb3 = set<tb3>;
#define rep0(TMS) for (int CNT = 0; CNT < (int)(TMS); CNT++)
#define rep(CNT, GOAL) for (int CNT = 0; CNT < (int)(GOAL); CNT++)
#define rep2(CNT, START, GOAL)                                                 \\
  for (int CNT = (int)(START); CNT < (int)(GOAL); CNT++)
#define rep3(CNT, START, GOAL)                                                 \\
  for (int CNT = (int)(START); CNT > (int)(GOAL); CNT--)
#define all(CONT) begin(CONT), end(CONT)
#define fr1(CONT) next(begin(CONT)), end(CONT)
#define itrep(ITR, CONT) for (auto ITR = begin(CONT); ITR != end(CONT); ITR++)
#define itrep1(ITR, CONT)                                                      \\
  for (auto ITR = next(begin(CONT)); ITR != end(CONT); ITR++)
#define maxel(CONT) *max_element(all(CONT))
#define minel(CONT) *min_element(all(CONT))
template <typename T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> T sum(const vector<T> &VEC) {
  return accumulate(all(VEC), 0.0);
}
template <typename T> vector<T> acm(const vector<T> &VEC) {
  vector<T> RES(VEC.size() + 1);
  rep(CNT, VEC.size()) RES[CNT + 1] = RES[CNT] + VEC[CNT];
  return RES;
}
template <typename T> void fil(vector<T> &VEC, const int NUM, const T &VAL) {
  VEC.assign(NUM, VAL);
}
template <typename T> void fil(vector<T> &VEC, const int NUM) {
  VEC.assign(NUM, 0.0);
}
template <typename T>
void fil(vector<vector<T>> &VV, const int RNUM, const int CNUM, const T &VAL) {
  fil(VV, RNUM, vector<T>());
  rep(CNT, RNUM) fil(VV[CNT], CNUM, VAL);
}
template <typename T>
void fil(vector<vector<T>> &VV, const int RNUM, const int CNUM) {
  fil(VV, RNUM, vector<T>());
  rep(CNT, RNUM) fil(VV[CNT], CNUM);
}
template <typename T> void fil(vector<vector<T>> &VV, const int RNUM) {
  fil(VV, RNUM, vector<T>());
}
void prec(const int &DIG) {
  cerr << fixed << setprecision(DIG);
  cout << fixed << setprecision(DIG);
}
template <typename T> void COUT(const T &ELEM) { cout << ELEM; }
template <typename T> void pout(const T &ELEM) {
  COUT(ELEM);
  cout << " ";
}
template <typename T, typename... Ts>
void pout(const T &FIRST, const Ts &...REST) {
  pout(FIRST);
  pout(REST...);
}
template <typename T> void print(T ELEM) {
  COUT(ELEM);
  cout << "\\n";
}
template <typename T, typename... Ts>
void print(const T &FIRST, const Ts &...REST) {
  print(FIRST);
  print(REST...);
}
void CERR() { cerr << "\\n"; }
template <typename T> void CERR(const T &ELEM) { cerr << ELEM; }
template <typename T, typename... Ts>
void CERR(const T &FIRST, const Ts &...REST) {
  CERR(FIRST);
  cerr << ", ";
  CERR(REST...);
}
template <typename T1, typename T2> void CERR(const pair<T1, T2> &PAIR) {
  cerr << "(";
  CERR(PAIR.first);
  cerr << ", ";
  CERR(PAIR.second);
  cerr << ")";
}
template <typename T1, typename T2, typename T3>
void CERR(const tuple<T1, T2, T3> &TUP3) {
  cerr << "(";
  CERR(get<0>(TUP3));
  cerr << ", ";
  CERR(get<1>(TUP3));
  cerr << ", ";
  CERR(get<2>(TUP3));
  cerr << ")";
}
template <typename T1, typename T2, typename T3, typename T4>
void CERR(const tuple<T1, T2, T3, T4> &TUP4) {
  cerr << "(";
  CERR(get<0>(TUP4));
  cerr << ", ";
  CERR(get<1>(TUP4));
  cerr << ", ";
  CERR(get<2>(TUP4));
  cerr << ", ";
  CERR(get<3>(TUP4));
  cerr << ")";
}
template <typename T> void CERR(const vector<T> &VEC) {
  cerr << "{ ";
  itrep(ITR, VEC) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T> void CERR1(const vector<T> &VEC) {
  cerr << "{ ";
  itrep1(ITR, VEC) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T> void CERR(const set<T> &SET) {
  cerr << "{ ";
  itrep(ITR, SET) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T1, typename T2> void CERR(const map<T1, T2> &MAP) {
  cerr << "{ ";
  itrep(ITR, MAP) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
#define db(OBJ)                                                                \\
  cerr << #OBJ << ": ";                                                        \\
  CERR(OBJ);                                                                   \\
  cerr << ", "
#define dbl(OBJ)                                                               \\
  cerr << #OBJ << ": ";                                                        \\
  CERR(OBJ);                                                                   \\
  cerr << "\\n"
#define db1(OBJ)                                                               \\
  cerr << #OBJ << ": ";                                                        \\
  CERR1(OBJ);                                                                  \\
  cerr << "\\n"
#define dbs(...)                                                               \\
  cerr << "(" << #__VA_ARGS__ << "): (";                                       \\
  CERR(__VA_ARGS__);                                                           \\
  cerr << ")\\n"
#define dbvv(VV)                                                               \\
  cerr << #VV << ": {\\n";                                                      \\
  rep(CNT, VV.size()) {                                                        \\
    cerr << #VV << "[" << CNT << "]: ";                                        \\
    CERR(VV[CNT]);                                                             \\
    cerr << ",\\n";                                                             \\
  }                                                                            \\
  cerr << "}\\n"
#define db01(VV)                                                               \\
  cerr << #VV << ": {\\n";                                                      \\
  rep(CNT, VV.size()) {                                                        \\
    cerr << #VV << "[" << CNT << "]: ";                                        \\
    CERR1(VV[CNT]);                                                            \\
    cerr << ",\\n";                                                             \\
  }                                                                            \\
  cerr << "}\\n"
#define db10(VV)                                                               \\
  cerr << #VV << ": {\\n";                                                      \\
  rep2(CNT, 1, VV.size()) {                                                    \\
    cerr << #VV << "[" << CNT << "]: ";                                        \\
    CERR(VV[CNT]);                                                             \\
    cerr << ",\\n";                                                             \\
  }                                                                            \\
  cerr << "}\\n"
#define db11(VV)                                                               \\
  cerr << #VV << ": {\\n";                                                      \\
  rep2(CNT, 1, VV.size()) {                                                    \\
    cerr << #VV << "[" << CNT << "]: ";                                        \\
    CERR1(VV[CNT]);                                                            \\
    cerr << ",\\n";                                                             \\
  }                                                                            \\
  cerr << "}\\n"
#define YN(FLG) cout << (FLG ? "YES" : "NO") << "\\n"
#define Yn(FLG) cout << (FLG ? "Yes" : "No") << "\\n"
#define yn(FLG) cout << (FLG ? "yes" : "no") << "\\n"
#define pcase(NUM)                                                             \\
  cout << "Case #" << NUM << ":"                                               \\
       << " "
#define pcasel(NUM)                                                            \\
  cout << "Case #" << NUM << ":"                                               \\
       << "\\n"
// const ll INF = 1'000'000'000'000'000'007;
const int INF = 1'000'000'007;
const ll MOD = 1'000'000'007; // 998'2447'353;

int main() {
  int N, M;
  cin >> N >> M;
  int x = 1, y = N;
  si ds;
  rep0(M) {
    while (ds.count(y - x) or ds.count(x + N - y) or y - x == x + N - y)
      y--;
    cout << x << " " << y << endl;
    ds.insert(y - x);
    ds.insert(x + N - y);
    x++;
    y--;
  }
}

Error: TLE

Fixed submission:

#define _GLIBCXX_DEBUG
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pdd = pair<double, double>;
using pss = pair<string, string>;
using pcc = pair<char, char>;
using pbb = pair<bool, bool>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using ti3 = tuple<int, int, int>;
using tl3 = tuple<ll, ll, ll>;
using td3 = tuple<double, double, double>;
using ts3 = tuple<string, string, string>;
using tc3 = tuple<char, char, char>;
using tb3 = tuple<bool, bool, bool>;
using ti4 = tuple<int, int, int, int>;
using tl4 = tuple<ll, ll, ll, ll>;
using td4 = tuple<double, double, double, double>;
using ts4 = tuple<string, string, string, string>;
using tc4 = tuple<char, char, char, char>;
using tb4 = tuple<bool, bool, bool, bool>;
using vi = vector<int>;
using vl = vector<ll>;
using vd = vector<double>;
using vs = vector<string>;
using vc = vector<char>;
using vb = vector<bool>;
using vvi = vector<vi>;
using vvl = vector<vl>;
using vvd = vector<vd>;
using vvs = vector<vs>;
using vvc = vector<vc>;
using vvb = vector<vb>;
using vvvi = vector<vvi>;
using vvvl = vector<vvl>;
using vvvd = vector<vvd>;
using vvvs = vector<vvs>;
using vvvc = vector<vvc>;
using vvvb = vector<vvb>;
using vpii = vector<pii>;
using vpll = vector<pll>;
using vpdd = vector<pdd>;
using vpss = vector<pss>;
using vpcc = vector<pcc>;
using vpbb = vector<pbb>;
using vpil = vector<pil>;
using vpli = vector<pli>;
using vti3 = vector<ti3>;
using vtl3 = vector<tl3>;
using vtd3 = vector<td3>;
using vts3 = vector<ts3>;
using vtc3 = vector<tc3>;
using vtb3 = vector<tb3>;
using vti4 = vector<ti4>;
using vtl4 = vector<tl4>;
using vtd4 = vector<td4>;
using vts4 = vector<ts4>;
using vtc4 = vector<tc4>;
using vtb4 = vector<tb4>;
using mii = map<int, int>;
using mll = map<ll, ll>;
using msi = map<string, int>;
using mci = map<char, int>;
using mil = map<int, ll>;
using mli = map<ll, int>;
using si = set<int>;
using sl = set<ll>;
using sd = set<double>;
using ss = set<string>;
using sc = set<char>;
using sb = set<bool>;
using spii = set<pii>;
using spll = set<pll>;
using spdd = set<pdd>;
using spss = set<pss>;
using spcc = set<pcc>;
using spbb = set<pbb>;
using spil = set<pil>;
using spli = set<pli>;
using sti3 = set<ti3>;
using stl3 = set<tl3>;
using std3 = set<td3>;
using sts3 = set<ts3>;
using stc3 = set<tc3>;
using stb3 = set<tb3>;
#define rep0(TMS) for (int CNT = 0; CNT < (int)(TMS); CNT++)
#define rep(CNT, GOAL) for (int CNT = 0; CNT < (int)(GOAL); CNT++)
#define rep2(CNT, START, GOAL)                                                 \\
  for (int CNT = (int)(START); CNT < (int)(GOAL); CNT++)
#define rep3(CNT, START, GOAL)                                                 \\
  for (int CNT = (int)(START); CNT > (int)(GOAL); CNT--)
#define all(CONT) begin(CONT), end(CONT)
#define fr1(CONT) next(begin(CONT)), end(CONT)
#define itrep(ITR, CONT) for (auto ITR = begin(CONT); ITR != end(CONT); ITR++)
#define itrep1(ITR, CONT)                                                      \\
  for (auto ITR = next(begin(CONT)); ITR != end(CONT); ITR++)
#define maxel(CONT) *max_element(all(CONT))
#define minel(CONT) *min_element(all(CONT))
template <typename T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> T sum(const vector<T> &VEC) {
  return accumulate(all(VEC), 0.0);
}
template <typename T> vector<T> acm(const vector<T> &VEC) {
  vector<T> RES(VEC.size() + 1);
  rep(CNT, VEC.size()) RES[CNT + 1] = RES[CNT] + VEC[CNT];
  return RES;
}
template <typename T> void fil(vector<T> &VEC, const int NUM, const T &VAL) {
  VEC.assign(NUM, VAL);
}
template <typename T> void fil(vector<T> &VEC, const int NUM) {
  VEC.assign(NUM, 0.0);
}
template <typename T>
void fil(vector<vector<T>> &VV, const int RNUM, const int CNUM, const T &VAL) {
  fil(VV, RNUM, vector<T>());
  rep(CNT, RNUM) fil(VV[CNT], CNUM, VAL);
}
template <typename T>
void fil(vector<vector<T>> &VV, const int RNUM, const int CNUM) {
  fil(VV, RNUM, vector<T>());
  rep(CNT, RNUM) fil(VV[CNT], CNUM);
}
template <typename T> void fil(vector<vector<T>> &VV, const int RNUM) {
  fil(VV, RNUM, vector<T>());
}
void prec(const int &DIG) {
  cerr << fixed << setprecision(DIG);
  cout << fixed << setprecision(DIG);
}
template <typename T> void COUT(const T &ELEM) { cout << ELEM; }
template <typename T> void pout(const T &ELEM) {
  COUT(ELEM);
  cout << " ";
}
template <typename T, typename... Ts>
void pout(const T &FIRST, const Ts &...REST) {
  pout(FIRST);
  pout(REST...);
}
template <typename T> void print(T ELEM) {
  COUT(ELEM);
  cout << "\\n";
}
template <typename T, typename... Ts>
void print(const T &FIRST, const Ts &...REST) {
  print(FIRST);
  print(REST...);
}
void CERR() { cerr << "\\n"; }
template <typename T> void CERR(const T &ELEM) { cerr << ELEM; }
template <typename T, typename... Ts>
void CERR(const T &FIRST, const Ts &...REST) {
  CERR(FIRST);
  cerr << ", ";
  CERR(REST...);
}
template <typename T1, typename T2> void CERR(const pair<T1, T2> &PAIR) {
  cerr << "(";
  CERR(PAIR.first);
  cerr << ", ";
  CERR(PAIR.second);
  cerr << ")";
}
template <typename T1, typename T2, typename T3>
void CERR(const tuple<T1, T2, T3> &TUP3) {
  cerr << "(";
  CERR(get<0>(TUP3));
  cerr << ", ";
  CERR(get<1>(TUP3));
  cerr << ", ";
  CERR(get<2>(TUP3));
  cerr << ")";
}
template <typename T1, typename T2, typename T3, typename T4>
void CERR(const tuple<T1, T2, T3, T4> &TUP4) {
  cerr << "(";
  CERR(get<0>(TUP4));
  cerr << ", ";
  CERR(get<1>(TUP4));
  cerr << ", ";
  CERR(get<2>(TUP4));
  cerr << ", ";
  CERR(get<3>(TUP4));
  cerr << ")";
}
template <typename T> void CERR(const vector<T> &VEC) {
  cerr << "{ ";
  itrep(ITR, VEC) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T> void CERR1(const vector<T> &VEC) {
  cerr << "{ ";
  itrep1(ITR, VEC) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T> void CERR(const set<T> &SET) {
  cerr << "{ ";
  itrep(ITR, SET) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T1, typename T2> void CERR(const map<T1, T2> &MAP) {
  cerr << "{ ";
  itrep(ITR, MAP) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
#define db(OBJ)                                                                \\
  cerr << #OBJ << ": ";                                                        \\
  CERR(OBJ);                                                                   \\
  cerr << ", "
#define dbl(OBJ)                                                               \\
  cerr << #OBJ << ": ";                                                        \\
  CERR(OBJ);                                                                   \\
  cerr << "\\n"
#define db1(OBJ)                                                               \\
  cerr << #OBJ << ": ";                                                        \\
  CERR1(OBJ);                                                                  \\
  cerr << "\\n"
#define dbs(...)                                                               \\
  cerr << "(" << #__VA_ARGS__ << "): (";                                       \\
  CERR(__VA_ARGS__);                                                           \\
  cerr << ")\\n"
#define dbvv(VV)                                                               \\
  cerr << #VV << ": {\\n";                                                      \\
  rep(CNT, VV.size()) {                                                        \\
    cerr << #VV << "[" << CNT << "]: ";                                        \\
    CERR(VV[CNT]);                                                             \\
    cerr << ",\\n";                                                             \\
  }                                                                            \\
  cerr << "}\\n"
#define db01(VV)                                                               \\
  cerr << #VV << ": {\\n";                                                      \\
  rep(CNT, VV.size()) {                                                        \\
    cerr << #VV << "[" << CNT << "]: ";                                        \\
    CERR1(VV[CNT]);                                                            \\
    cerr << ",\\n";                                                             \\
  }                                                                            \\
  cerr << "}\\n"
#define db10(VV)                                                               \\
  cerr << #VV << ": {\\n";                                                      \\
  rep2(CNT, 1, VV.size()) {                                                    \\
    cerr << #VV << "[" << CNT << "]: ";                                        \\
    CERR(VV[CNT]);                                                             \\
    cerr << ",\\n";                                                             \\
  }                                                                            \\
  cerr << "}\\n"
#define db11(VV)                                                               \\
  cerr << #VV << ": {\\n";                                                      \\
  rep2(CNT, 1, VV.size()) {                                                    \\
    cerr << #VV << "[" << CNT << "]: ";                                        \\
    CERR1(VV[CNT]);                                                            \\
    cerr << ",\\n";                                                             \\
  }                                                                            \\
  cerr << "}\\n"
#define YN(FLG) cout << (FLG ? "YES" : "NO") << "\\n"
#define Yn(FLG) cout << (FLG ? "Yes" : "No") << "\\n"
#define yn(FLG) cout << (FLG ? "yes" : "no") << "\\n"
#define pcase(NUM)                                                             \\
  cout << "Case #" << NUM << ":"                                               \\
       << " "
#define pcasel(NUM)                                                            \\
  cout << "Case #" << NUM << ":"                                               \\
       << "\\n"
// const ll INF = 1'000'000'000'000'000'007;
const int INF = 1'000'000'007;
const ll MOD = 1'000'000'007; // 998'2447'353;

int main() {
  int N, M;
  cin >> N >> M;
  int x = 1, y = N;
  si ds;
  rep0(M) {
    int d1 = y - x, d2 = x + N - y;
    while (ds.count(d1) or ds.count(d2) or d1 == d2)
      y--;
    cout << x << " " << y << endl;
    ds.insert(d1);
    ds.insert(d2);
    x++;
    y--;
  }
}