foo.cc: In function 'bool SPFA(int, int)':
foo.cc:97:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int z = 0; z < edge[x].size(); z++)
                         ~~^~~~~~~~~~~~~~~~
foo.cc: In function 'newpair ZKW_DFS(int, int, int)':
foo.cc:158:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int& z = head[x]; z < edge[x].size(); z++)
                            ~~^~~~~~~~~~~~~~~~
foo.cc: In function 'void costflow()':
foo.cc:187:20: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
         while (ans = ZKW_DFS(0, st, inf))
                ~~~~^~~~~~~~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:228:40: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     for (int i = 1; i <= n; i++)  scanf("%lf", &A[i]);
                                   ~~~~~^~~~~~~~~~~~~~
foo.cc:247:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%lf%d", &cost, &flow);
         ~~~~~^~~~~~~~~~~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。