Language: C++

#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<bits/stdc++.h>
#include<cmath>
#include<bitset>
#include<queue>
#define ll long long
#define itn int
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define FFOR(i,a,b) for(int i=(a);i<=(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define RREP(i,n)  FFOR(i,1,n)
#define SORT(V) sort((V).begin(),(V).end())
#define REVERSE(V) reverse((V).begin(),(V).end())
#define INF ((1LL<<62)-(1LL<<31))
#define MOD 1000000007
using namespace std;

int main(){
  string S;
  int K;
  cin>>S>>K;
  
  int N=S.size();
  set<string> L;
  
  for(int i=1; i<=K; ++i){
    for(int j=0; j<=N-i; ++j){
      L.push_back(S.substr(j,i));
    }
  }
  
  SORT(L);
  cout<<L.at(K-1)<<endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:31:9: error: 'class std::set<std::__cxx11::basic_string<char> >' has no member named 'push_back'
   31 |       L.push_back(S.substr(j,i));
      |         ^~~~~~~~~
a.cc:36:11: error: 'class std::set<std::__cxx11::basic_string<char> >' has no member named 'at'
   36 |   cout<<L.at(K-1)<<endl;
      |           ^~
In file included from /usr/include/c++/14/algorithm:61,
                 from a.cc:4:
/usr/include/c++/14/bits/stl_algo.h: In instantiation of 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = _Rb_tree_const_iterator<__cxx11::basic_string<char> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]':
/usr/include/c++/14/bits/stl_algo.h:4772:18:   required from 'void std::sort(_RAIter, _RAIter) [with _RAIter = _Rb_tree_const_iterator<__cxx11::basic_string<char> >]'
 4772 |       std::__sort(__first, __last, __gnu_cxx::__ops::__iter_less_iter());
      |       ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cc:35:3:   required from here
   15 | #define SORT(V) sort((V).begin(),(V).end())
      |                 ~~~~^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:1906:50: error: no match for 'operator-' (operand types are 'std::_Rb_tree_const_iterator<std::__cxx11::basic_string<char> >' and 'std::_Rb_tree_const_iterator<std::__cxx11::basic_string<char> >')
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
In file included from /usr/include/c++/14/string:48,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_iterator.h:618:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__y.base() - __x.base())) std::operator-(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  618 |     operator-(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:618:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_Rb_tree_const_iterator<std::__cxx11::basic_string<char> >' is not derived from 'const std::reverse_iterator<_Iterator>'
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__x.base() - __y.base())) std::operator-(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1790 |     operator-(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_Rb_tree_const_iterator<std::__cxx11::basic_string<char> >' is not derived from 'const std::move_iterator<_IteratorL>'
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166,
                 from a.cc:5:
/usr/include/c++/14/valarray:1197:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__minus, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__minus, _Tp>::result_type> std::operator-(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)'
 1197 | _DEFINE_BINARY_OPERATOR(-, __minus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1197:1: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_Rb_tree_const_iterator<std::__cxx11::basic_string<char> >' is not derived from 'const std::valarray<_Tp>'
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
/usr/include/c++/14/valarray:1197:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__minus, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__minus, _Tp>::result_type> std::operator-(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)'
 1197 | _DEFINE_BINARY_OPERATOR(-, __minus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1197:1: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_Rb_tree_const_iterator<std::__cxx11::basic_string<char> >' is not derived from 'const std::valarray<_Tp>'
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
/usr/include/c++/14/valarray:1197:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__minus, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__minus, _Tp>::result_type> std::operator-(const valarray<_Tp>&, const valarray<_Tp>&)'
 1197 | _DEFINE_BINARY_OPERATOR(-, __minus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1197:1: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_Rb_tree_const_iterator<std::__cxx11::basic_string<char> >' is not derived from 'const std::valarray<_Tp>'
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
In file included from /usr/include/c++/14/valarray:605:
/usr/include/c++/14/bits/valarray_after.h:406:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__minus, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  406 |     _DEFINE_EXPR_BINARY_OPERATOR(-, struct std::__minus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_Rb_tree_const_iterator<std::__cxx11::basic_string<char> >' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__minus, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)'
  406 |     _DEFINE_EXPR_BINARY_OPERATOR(-, struct std::__minus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_Rb_tree_const_iterator<std::__cxx11::basic_string<char> >' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__minus, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  406 |     _DEFINE_EXPR_BINARY_OPERATOR(-, struct std::__minus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_Rb_tree_const_iterator<std::__cxx11::basic_string<char> >' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__minus, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)'
  406 |     _DEFINE_EXPR_BINARY_OPERATOR(-, struct std::__minus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_Rb_tree_const_iterator<std::__cxx11::basic_string<char> >' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note: candidate: 'template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__minus, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)'
  406 |     _DEFINE_EXPR_BINARY_OPERATOR(-, struct std::__minus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_Rb_tre