Compilare: main.cpp: In function 'int main()': main.cpp:33:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 33 | for (int j = 0; j < s[i].size(); ++j) { | ~~^~~~~~~~~~~~~ In file included from /usr/include/c++/12.2.1/string:53, from /usr/include/c++/12.2.1/bits/locale_classes.h:40, from /usr/include/c++/12.2.1/bits/ios_base.h:41, from /usr/include/c++/12.2.1/ios:42, from /usr/include/c++/12.2.1/ostream:38, from /usr/include/c++/12.2.1/iostream:39, from main.cpp:1: In member function 'constexpr std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]', inlined from 'void backtrack(int, int)' at main.cpp:21:38: /usr/include/c++/12.2.1/bits/basic_string.h:1064:16: warning: iteration 2 invokes undefined behavior [-Waggressive-loop-optimizations] 1064 | { return _M_string_length; } | ^~~~~~~~~~~~~~~~ main.cpp: In function 'void backtrack(int, int)': main.cpp:20:23: note: within this loop 20 | for (int i = 1; i <= 3; ++i) { | ~~^~~~ In member function 'constexpr std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]', inlined from 'void backtrack(int, int)' at main.cpp:24:48: /usr/include/c++/12.2.1/bits/basic_string.h:1064:16: warning: iteration 2 invokes undefined behavior [-Waggressive-loop-optimizations] 1064 | { return _M_string_length; } | ^~~~~~~~~~~~~~~~ main.cpp: In function 'void backtrack(int, int)': main.cpp:23:23: note: within this loop 23 | for (int i = 1; i <= 3; ++i) { | ~~^~~~ In member function 'constexpr std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]', inlined from 'int main()' at main.cpp:33:38: /usr/include/c++/12.2.1/bits/basic_string.h:1064:16: warning: iteration 2 invokes undefined behavior [-Waggressive-loop-optimizations] 1064 | { return _M_string_length; } | ^~~~~~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:32:23: note: within this loop 32 | for (int i = 1; i <= 3; ++i) { | ~~^~~~