/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:9:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if(n == s.length()){
        ~~^~~~~~~~~~~~~
/in/foo.cc:19:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if(n < s.length()-1){
        ~~^~~~~~~~~~~~~~