foo.cpp: In function 'void bfs_fan()':
foo.cpp:20:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0;i<X[Q[head]].size();i++)
              ^
foo.cpp:13:9: warning: unused variable 'j' [-Wunused-variable]
   int i,j,k,head,tail;
         ^
foo.cpp: In function 'int bfs_zheng()':
foo.cpp:43:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0;i<X[j].size();i++)
              ^
foo.cpp: In function 'int main()':
foo.cpp:68:19: error: 'system' was not declared in this scope
     system("pause");
                   ^
foo.cpp:57:11: warning: unused variable 'j' [-Wunused-variable]
     int i,j,x,y,m,n;
           ^