train.cpp: In function 'int dfs(int, bool)':
train.cpp:35:3: error: use of an operand of type 'bool' in 'operator++' is forbidden in C++17
35 | charging++;
| ^~~~~~~~
train.cpp: In function 'std::vector<int> who_wins(std::vector<int>, std::vector<int>, std::vector<int>, std::vector<int>)':
train.cpp:49:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
49 | for (int i = 0; i < a.size(); i++)
| ~~^~~~~~~~~~
train.cpp:54:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
54 | for (int i = 0; i < u.size(); i++)
| ~~^~~~~~~~~~
train.cpp:62:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
62 | for (int i = 0; i < a.size(); i++)
| ~~^~~~~~~~~~