/in/foo.cc: In function 'bool spfa(int)':
/in/foo.cc:14:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<g[u].size();i++){
               ~^~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:38:8: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   mid=l+r>>1;
       ~^~