/in/foo.cc: In function 'void SPFA(int)':
/in/foo.cc:56:9: warning: unused variable 'hea' [-Wunused-variable]
     int hea=1,tail=1;
         ^~~
/in/foo.cc:56:15: warning: unused variable 'tail' [-Wunused-variable]
     int hea=1,tail=1;
               ^~~~