/in/foo.cc:5: error: unterminated #ifdef
    5 | #ifdef method_1
      | 
/in/foo.cc: In function 'int dfs(int, int, int)':
/in/foo.cc:30:8: warning: control reaches end of non-void function [-Wreturn-type]
   30 |     dfs(x+1,used+1,now^a[x]);
      |     ~~~^~~~~~~~~~~~~~~~~~~~~