foo.cc: In function 'int Dijkstra(int, int)':
foo.cc:41:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0; i<edge[u].size(); i++) {
                      ~^~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:58:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d",&a,&b);
     ~~~~~^~~~~~~~~~~~~~

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