Problem p02697 (C++)

Buggy submission (status: Time Limit Exceeded):
// #pragma comment(linker, "/stack:200000000")
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize(3)
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
// #pragma GCC target("sse3","sse2","sse")
// #pragma GCC target("avx","sse4","sse4.1","sse4.2","ssse3")
// #pragma GCC target("f16c")
// #pragma GCC
// optimize("inline","fast-math","unroll-loops","no-stack-protector") #pragma
// GCC diagnostic error "-fwhole-program" #pragma GCC diagnostic error
// "-fcse-skip-blocks" #pragma GCC diagnostic error
// "-funsafe-loop-optimizations" #pragma GCC diagnostic error "-std=c++14"
#include "bits/stdc++.h"
#include "ext/pb_ds/assoc_container.hpp"
#include "ext/pb_ds/tree_policy.hpp"

#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fr(x) freopen(x, "r", stdin)
#define fw(x) freopen(x, "w", stdout)
#define iout(x) printf("%d\n", x)
#define lout(x) printf("%lld\n", x)
#define REP(x, l, u) for (ll x = l; x < u; x++)
#define RREP(x, l, u) for (ll x = l; x >= u; x--)
#define complete_unique(a) a.erase(unique(a.begin(), a.end()), a.end())
#define mst(x, a) memset(x, a, sizeof(x))
#define all(a) begin(a), end(a)
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define MP make_pair
#define lowbit(x) ((x) & (-(x)))
#define bitcnt(x) (__builtin_popcountll(x))
#define lson (ind << 1)
#define rson (ind << 1 | 1)
#define se second
#define fi first
#define sz(x) ((int)x.size())
#define EX0 exit(0);

typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;
using namespace __gnu_pbds; // required
using namespace std;
template <typename T>
using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef vector<ll> VLL;
typedef vector<int> VI;
const int block_size = 320;
typedef complex<ll> point;
const ll mod = 1e9 + 7;
const ll inf = 1e9 + 7;
const ld eps = 1e-9;
const db PI = atan(1) * 4;

template <typename T> inline int sign(const T &a) {
  if (a < 0)
    return -1;
  if (a > 0)
    return 1;
  return 0;
}

string to_string(string s) { return '"' + s + '"'; }

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

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

template <typename A, typename B> string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A> string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

void debug_out() { cerr << endl; }

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

#ifndef ONLINE_JUDGE
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define dbg(...)                                                               \
  {}
#endif

template <typename T, typename S> inline bool upmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}

template <typename T, typename S> inline bool upmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}

template <typename T> inline void in(T &x) {
  x = 0;
  T f = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-')
      f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  x *= f;
}

ull twop(ll x) { return 1ULL << x; }

ll MOD(ll a, ll m) {
  a %= m;
  if (a < 0)
    a += m;
  return a;
}

ll inverse(ll a, ll m) {
  a = MOD(a, m);
  if (a <= 1)
    return a;
  return MOD((1 - inverse(m, a) * m) / a, m);
}

template <typename A, typename B> inline void in(A &x, B &y) {
  in(x);
  in(y);
}

template <typename A, typename B, typename C> inline void in(A &x, B &y, C &z) {
  in(x);
  in(y);
  in(z);
}

template <typename A, typename B, typename C, typename D>
inline void in(A &x, B &y, C &z, D &d) {
  in(x);
  in(y);
  in(z);
  in(d);
}

template <typename T> T sqr(T x) { return x * x; }

ll gcd(ll a, ll b) {
  while (b != 0) {
    a %= b;
    swap(a, b);
  }
  return abs(a);
}

ll fast(ll a, ll b, ll mod) {
  if (b < 0)
    a = inverse(a, mod), b = -b;
  ll ans = 1;
  while (b) {
    if (b & 1) {
      b--;
      ans = ans * a % mod;
    } else {
      a = a * a % mod;
      b /= 2;
    }
  }
  return ans % mod;
}

namespace SOLVE {
ll n, m;
void test(vector<PLL> prs, ll n) {
  vector<char> v(n);
  REP(i, 0, n) v[i] = i + 'A';
  map<pair<char, char>, ll> cnt;
  REP(i, 0, n) {
    for (auto [a, b] : prs) {
      cnt[MP(min(v[a - 1], v[b - 1]), max(v[a - 1], v[b - 1]))]++;
      cerr << v[a - 1] << " " << v[b - 1] << " " << a << " " << b << endl;
    }
    v.insert(begin(v), v.back());
    v.pop_back();
    cerr << "--------\n";
  }
  for (auto i : cnt)
    assert(i.se == 1);
}

void odd() {
  ll l = n / 2, r = n / 2 + 1;
  vector<PLL> v;
  REP(i, 0, m) {
    cout << l << " " << r << endl;
    v.PB({l, r});
    l--;
    r++;
  }
  test(v, n);
}

void even() {
  vector<PLL> v;
  ll l = n / 2, r = n / 2 + 1;
  REP(i, 0, m) {
    if (r - l == n / 2 or r - l == n / 2 + 1)
      l--;
    v.push_back(make_pair(l, r));
    l--;
    r++;
  }
  //        test(v,n);
  for (auto i : v)
    cout << i.fi << " " << i.se << endl;
}

void main() {
  in(n, m);
  if (n % 2 == 0)
    even();
  else
    odd();
}
} // namespace SOLVE

signed main() {
#ifndef ONLINE_JUDGE
  fr("/Users/zhangqingchuan/Desktop/cp/cp/input.txt");
  fw("/Users/zhangqingchuan/Desktop/cp/cp/output.txt");
#endif

  int t = 1;
  //    in(t);
  for (int i = 1; i <= t; i++) {
    //        cout<<"Case #"<<i<<":";
    SOLVE::main();
  }

  //    clock_t st = clock();
  //    while(clock() - st < 3.0 * CLOCKS_PER_SEC){
  //
  //    }

  return 0;
}


Fixed submission:
// #pragma comment(linker, "/stack:200000000")
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize(3)
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
// #pragma GCC target("sse3","sse2","sse")
// #pragma GCC target("avx","sse4","sse4.1","sse4.2","ssse3")
// #pragma GCC target("f16c")
// #pragma GCC
// optimize("inline","fast-math","unroll-loops","no-stack-protector") #pragma
// GCC diagnostic error "-fwhole-program" #pragma GCC diagnostic error
// "-fcse-skip-blocks" #pragma GCC diagnostic error
// "-funsafe-loop-optimizations" #pragma GCC diagnostic error "-std=c++14"
#include "bits/stdc++.h"
#include "ext/pb_ds/assoc_container.hpp"
#include "ext/pb_ds/tree_policy.hpp"

#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fr(x) freopen(x, "r", stdin)
#define fw(x) freopen(x, "w", stdout)
#define iout(x) printf("%d\n", x)
#define lout(x) printf("%lld\n", x)
#define REP(x, l, u) for (ll x = l; x < u; x++)
#define RREP(x, l, u) for (ll x = l; x >= u; x--)
#define complete_unique(a) a.erase(unique(a.begin(), a.end()), a.end())
#define mst(x, a) memset(x, a, sizeof(x))
#define all(a) begin(a), end(a)
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define MP make_pair
#define lowbit(x) ((x) & (-(x)))
#define bitcnt(x) (__builtin_popcountll(x))
#define lson (ind << 1)
#define rson (ind << 1 | 1)
#define se second
#define fi first
#define sz(x) ((int)x.size())
#define EX0 exit(0);

typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;
using namespace __gnu_pbds; // required
using namespace std;
template <typename T>
using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef vector<ll> VLL;
typedef vector<int> VI;
const int block_size = 320;
typedef complex<ll> point;
const ll mod = 1e9 + 7;
const ll inf = 1e9 + 7;
const ld eps = 1e-9;
const db PI = atan(1) * 4;

template <typename T> inline int sign(const T &a) {
  if (a < 0)
    return -1;
  if (a > 0)
    return 1;
  return 0;
}

string to_string(string s) { return '"' + s + '"'; }

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

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

template <typename A, typename B> string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A> string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

void debug_out() { cerr << endl; }

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

#ifndef ONLINE_JUDGE
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define dbg(...)                                                               \
  {}
#endif

template <typename T, typename S> inline bool upmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}

template <typename T, typename S> inline bool upmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}

template <typename T> inline void in(T &x) {
  x = 0;
  T f = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-')
      f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  x *= f;
}

ull twop(ll x) { return 1ULL << x; }

ll MOD(ll a, ll m) {
  a %= m;
  if (a < 0)
    a += m;
  return a;
}

ll inverse(ll a, ll m) {
  a = MOD(a, m);
  if (a <= 1)
    return a;
  return MOD((1 - inverse(m, a) * m) / a, m);
}

template <typename A, typename B> inline void in(A &x, B &y) {
  in(x);
  in(y);
}

template <typename A, typename B, typename C> inline void in(A &x, B &y, C &z) {
  in(x);
  in(y);
  in(z);
}

template <typename A, typename B, typename C, typename D>
inline void in(A &x, B &y, C &z, D &d) {
  in(x);
  in(y);
  in(z);
  in(d);
}

template <typename T> T sqr(T x) { return x * x; }

ll gcd(ll a, ll b) {
  while (b != 0) {
    a %= b;
    swap(a, b);
  }
  return abs(a);
}

ll fast(ll a, ll b, ll mod) {
  if (b < 0)
    a = inverse(a, mod), b = -b;
  ll ans = 1;
  while (b) {
    if (b & 1) {
      b--;
      ans = ans * a % mod;
    } else {
      a = a * a % mod;
      b /= 2;
    }
  }
  return ans % mod;
}

namespace SOLVE {
ll n, m;
void test(vector<PLL> prs, ll n) {
  vector<char> v(n);
  REP(i, 0, n) v[i] = i + 'A';
  map<pair<char, char>, ll> cnt;
  REP(i, 0, n) {
    for (auto [a, b] : prs) {
      cnt[MP(min(v[a - 1], v[b - 1]), max(v[a - 1], v[b - 1]))]++;
      cerr << v[a - 1] << " " << v[b - 1] << " " << a << " " << b << endl;
    }
    v.insert(begin(v), v.back());
    v.pop_back();
    cerr << "--------\n";
  }
  for (auto i : cnt)
    assert(i.se == 1);
}

void odd() {
  ll l = n / 2, r = n / 2 + 1;
  vector<PLL> v;
  REP(i, 0, m) {
    cout << l << " " << r << endl;
    v.PB({l, r});
    l--;
    r++;
  }
  //        test(v,n);
}

void even() {
  vector<PLL> v;
  ll l = n / 2, r = n / 2 + 1;
  REP(i, 0, m) {
    if (r - l == n / 2 or r - l == n / 2 + 1)
      l--;
    v.push_back(make_pair(l, r));
    l--;
    r++;
  }
  //        test(v,n);
  for (auto i : v)
    cout << i.fi << " " << i.se << endl;
}

void main() {
  in(n, m);
  if (n % 2 == 0)
    even();
  else
    odd();
}
} // namespace SOLVE

signed main() {
#ifndef ONLINE_JUDGE
  fr("/Users/zhangqingchuan/Desktop/cp/cp/input.txt");
  fw("/Users/zhangqingchuan/Desktop/cp/cp/output.txt");
#endif

  int t = 1;
  //    in(t);
  for (int i = 1; i <= t; i++) {
    //        cout<<"Case #"<<i<<":";
    SOLVE::main();
  }

  //    clock_t st = clock();
  //    while(clock() - st < 3.0 * CLOCKS_PER_SEC){
  //
  //    }

  return 0;
}