Find unique duplicate values in rows

I need to locate and highlight duplicate values in several rows. I can use the =countif function, but it takes too much time to use it for 30 different rows!

Sample data:

1 2 3 4 5 6 7 8 1

2 3 4 5 6 1 7 8 3

1 2 3 4 8 5 6 7 8

I need to flag "1" in the first row; "3" in the second row & "8" in the third row.