/in/foo.cc: In function 'void spfa(int)':
/in/foo.cc:13:10: warning: unused variable 'np' [-Wunused-variable]
  int ind,np,x,i,head=0,tail=1,vv;
          ^~
/in/foo.cc:13:15: warning: unused variable 'i' [-Wunused-variable]
  int ind,np,x,i,head=0,tail=1,vv;
               ^