foo.cc: In function 'int dijkstra(int, int)':
foo.cc:26:63: warning: 'u' may be used uninitialized [-Wmaybe-uninitialized]
   26 |                                 if (arr[begin][j]>arr[begin][u] + arr[u][j])
      |                                                   ~~~~~~~~~~~~^
foo.cc:7:21: note: 'u' was declared here
    7 |         int s[2501],u;
      |                     ^

[Hydro](https://hydro.ac)提供评测服务