/in/foo.cc: In function 'bool SPFA(int)':
/in/foo.cc:35:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for( int i = 0 ; i < G[tx].size() ; i ++ ){
                          ~~^~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:71:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for( int i = 0 ; i < G[tx].size() ; i ++ ){
                          ~~^~~~~~~~~~~~~~