prepare (1/3): 
finished

make (2/3): 
g++ -g -Wall -O2 -o main.o -c main.cpp 
main.cpp: In function 'int main(int, const char**)':
main.cpp:73:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if (List.size() == node_num) cout << "The graph is a DAG" << endl;
         ~~~~~~~~~~~~^~~~~~~~~~~
g++ -g -Wall -O2 -o main main.o
finished

clean (3/3): 
finished

all task finished, build successfully