/in/foo.cc: In function 'int spfa()':
/in/foo.cc:21:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<g[x].size();i++)
               ~^~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:46:5: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
     for(int i=1;i<=n;i++)
     ^~~
/in/foo.cc:48:2: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
  for(int i=1;i<=m;i++)
  ^~~
/in/foo.cc: In function 'int spfa()':
/in/foo.cc:42:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^