foo.cc: In function 'int main()':
foo.cc:16:5: error: 'dfs' was not declared in this scope
     dfs(0, 0, 1);
     ^~~
foo.cc:13:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d", &n, &k);
     ~~~~~^~~~~~~~~~~~~~~~
foo.cc:15:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d", &a[i]);
         ~~~~~^~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务