/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:7:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if (history.size() == length) {
         ~~~~~~~~~~~~~~~^~~~~~~~~
/in/foo.cc:8:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < history.size(); i++)
                         ~~^~~~~~~~~~~~~~~~