check bottom - left cell
if ( ( elex < m - 1 ) && ( eley > 0 ) && ( rect [ elex + 1 ] [ eley - 1 ] == 0 ) ) { rect [ elex + 1 ] [ eley - 1 ] = 1 ; vector < int > v = { elex + 1 , eley - 1 } ; qu . push_back ( v ) ; }