/in/foo.cc: In function 'int main()':
/in/foo.cc:50:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 1; i < p.size(); i++) {
                    ~~^~~~~~~~~~
/in/foo.cc:51:22: error: no match for 'operator[]' (operand types are 'std::__cxx11::list<int>' and 'int')
         L.push_back(p[i] - p[i-1]);
                      ^
/in/foo.cc:51:29: error: no match for 'operator[]' (operand types are 'std::__cxx11::list<int>' and 'int')
         L.push_back(p[i] - p[i-1]);
                             ^
/in/foo.cc:53:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     while(L.size() > k) {
           ~~~~~~~~~^~~
In file included from /usr/include/c++/6/algorithm:62:0,
                 from /in/foo.cc:8:
/usr/include/c++/6/bits/stl_algo.h: In instantiation of 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = std::_List_iterator<int>; _Compare = __gnu_cxx::__ops::_Iter_less_iter]':
/usr/include/c++/6/bits/stl_algo.h:4707:18:   required from 'void std::sort(_RAIter, _RAIter) [with _RAIter = std::_List_iterator<int>]'
/in/foo.cc:47:28:   required from here
/usr/include/c++/6/bits/stl_algo.h:1966:22: error: no match for 'operator-' (operand types are 'std::_List_iterator<int>' and 'std::_List_iterator<int>')
     std::__lg(__last - __first) * 2,
               ~~~~~~~^~~~~~~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:2:
/usr/include/c++/6/bits/stl_iterator.h:333:5: note: candidate: template<class _Iterator> decltype ((__x.base() - __y.base())) std::operator-(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
     operator-(const reverse_iterator<_Iterator>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:333:5: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/6/algorithm:62:0,
                 from /in/foo.cc:8:
/usr/include/c++/6/bits/stl_algo.h:1966:22: note:   'std::_List_iterator<int>' is not derived from 'const std::reverse_iterator<_Iterator>'
     std::__lg(__last - __first) * 2,
               ~~~~~~~^~~~~~~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:2:
/usr/include/c++/6/bits/stl_iterator.h:387:5: note: candidate: template<class _IteratorL, class _IteratorR> decltype ((__y.base() - __x.base())) std::operator-(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)
     operator-(const reverse_iterator<_IteratorL>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:387:5: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/6/algorithm:62:0,
                 from /in/foo.cc:8:
/usr/include/c++/6/bits/stl_algo.h:1966:22: note:   'std::_List_iterator<int>' is not derived from 'const std::reverse_iterator<_Iterator>'
     std::__lg(__last - __first) * 2,
               ~~~~~~~^~~~~~~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:2:
/usr/include/c++/6/bits/stl_iterator.h:1186:5: note: candidate: template<class _IteratorL, class _IteratorR> decltype ((__x.base() - __y.base())) std::operator-(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&)
     operator-(const move_iterator<_IteratorL>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:1186:5: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/6/algorithm:62:0,
                 from /in/foo.cc:8:
/usr/include/c++/6/bits/stl_algo.h:1966:22: note:   'std::_List_iterator<int>' is not derived from 'const std::move_iterator<_IteratorL>'
     std::__lg(__last - __first) * 2,
               ~~~~~~~^~~~~~~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:2:
/usr/include/c++/6/bits/stl_iterator.h:1193:5: note: candidate: template<class _Iterator> decltype ((__x.base() - __y.base())) std::operator-(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorL>&)
     operator-(const move_iterator<_Iterator>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:1193:5: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/6/algorithm:62:0,
                 from /in/foo.cc:8:
/usr/include/c++/6/bits/stl_algo.h:1966:22: note:   'std::_List_iterator<int>' is not derived from 'const std::move_iterator<_IteratorL>'
     std::__lg(__last - __first) * 2,
               ~~~~~~~^~~~~~~~~