Language: C++

#include <bits/stdc++.h>
using namespace std;
#define repd(i,a,b) for (int i=a;i<int(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


signed main(){
  int n,k;cin>>n>>k;vector<int> vec, ans;
  int sum = 0, cnt = 0;
  while(sum < k && cnt < n){
    int c = 1;
    while(sum + c*(c-1)/2 <= k)c++;
    sum += (c-1)*(c-2)/2;
    cnt += c;
    vec.push_back(c);
  }
  if(cnt > n || sum < k){
    cout << -1 << endl;
    return 0;
  }
  int top = 0;
  for(auto i : vec){
    repd(j,1,i)ans.push_back(P(top+1,top+j+1));
    top += i;
  }
  cout << ans.size() << endl;
  for(auto p : ans)cout << p << endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:63:29: error: no matching function for call to 'std::vector<long long int>::push_back(P)'
   63 |     repd(j,1,i)ans.push_back(P(top+1,top+j+1));
      |                ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/vector:66,
                 from /usr/include/c++/14/functional:64,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:53,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_vector.h:1283:7: note: candidate: 'void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = long long int; _Alloc = std::allocator<long long int>; value_type = long long int]'
 1283 |       push_back(const value_type& __x)
      |       ^~~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1283:35: note:   no known conversion for argument 1 from 'P' {aka 'std::pair<long long int, long long int>'} to 'const std::vector<long long int>::value_type&' {aka 'const long long int&'}
 1283 |       push_back(const value_type& __x)
      |                 ~~~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:1300:7: note: candidate: 'void std::vector<_Tp, _Alloc>::push_back(value_type&&) [with _Tp = long long int; _Alloc = std::allocator<long long int>; value_type = long long int]'
 1300 |       push_back(value_type&& __x)
      |       ^~~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1300:30: note:   no known conversion for argument 1 from 'P' {aka 'std::pair<long long int, long long int>'} to 'std::vector<long long int>::value_type&&' {aka 'long long int&&'}
 1300 |       push_back(value_type&& __x)
      |                 ~~~~~~~~~~~~~^~~