C :: Replace Repeated Elements Within 2D (10x10) Int Array

I have generated a 10x10 integer matrix, by way of a 2 dimensional array, the elements are randomly generated and lie on 1 <= z <= 5. I am in need of an efficient method of setting all adjacent "duplicates" (repeating elements) of length 3 or greater to the integer six (6). The source for the brute method follows for clarity.

Code:
46 for(row=0;row<10;row++)
47 {
48 for(col=0;col<10;col++)
49 {
50 board[row][col]=rand()%4+1; //filling matrix here

[Code] .....

I know there must exist a much more elegant approach than listing out all permutations.