Two or more accessible links per post.

Hi,
I have so many categories in my site and my permalinks is that \%category%\%slug%, so if i have one post with 2 categories, like category-1 and category-2, its accessible by two links, category-1\%slug% and category-2\%slug%, it’s really bad for google or others indexes my site. How can i redirect the post for only one link? Via .htaccess maybe?

Thanks.