prepare (1/3): 
finished

make (2/3): 
g++ -std=c++11 -O2 -g -Wall -c main.cpp
main.cpp: In function 'void isDAG(Graph&, int)':
main.cpp:72:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if(List.size() == N) cout << "The graph is a DAG" << endl;
        ~~~~~~~~~~~~^~~~
main.cpp: In function 'void MST(Graph&)':
main.cpp:118:13: warning: unused variable 'key' [-Wunused-variable]
         int key = next_in->key;
             ^~~
g++ -std=c++11 -O2 -g -Wall -o main main.o
finished

clean (3/3): 
finished

all task finished, build successfully