foo.cc: In function 'void dfs(int)':
foo.cc:67:25: warning: 'y' may be used uninitialized in this function [-Wmaybe-uninitialized]
     int val=row[x]&col[y]&grid[g(x,y)];
                    ~~~~~^
foo.cc:74:16: warning: 'x' may be used uninitialized in this function [-Wmaybe-uninitialized]
         a[x][y]=-1;
         ~~~~~~~^~~

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