mark the available points
for i in range ( n ) : NEW_LINE INDENT m [ ( points [ i ] [ 0 ] , points [ i ] [ 1 ] ) ] = m . get ( ( points [ i ] [ 0 ] , points [ i ] [ 1 ] ) , 0 ) + 1 NEW_LINE DEDENT side = - 1 NEW_LINE x = - 1 NEW_LINE y = - 1 NEW_LINE