robot

function mark_x(r, points_arr)
    global pos marked
    global points
    points = points_arr;
    pos = [0, 0];
    marked = [];
    go_around(r)
end

function go_around(r)
    global pos marked
    if !ismember(pos, marked, 'rows')
        marked = [marked; pos];
        for s = 'nosw'
            if r.is_bord(s) == 0
                step(r, s)
                go_around(r)
                s = reverse(s);
                step(r, s)
            end
        end
    end
end

function step(r, s)
    global pos points
    r.step(s)
    switch s
        case 'n'
            pos(2)++;
        case 's'
            pos(2)--;
        case 'o'
            pos(1)++;
        case 'w'
            pos(1)--;
    end
    if ismember(pos, points, 'rows')
        r.mark()
    end
end

function s = reverse(s)
    switch s
        case 'n'
            s = 's';
        case 's'
            s = 'n';
        case 'o'
            s = 'w';
        case 'w'
            s = 'o';
    end
end