before output I check arrays:

    for(i = 0; i < n; i++)
        for(j = 1; j < m; j++)
            if( a[i][j-1] == a[i][j] && b[i][j-1] == b[i][j] )
                while(1);

    for(i = 1; i < n; i++)
        for(j = 0; j < m; j++)
            if( a[i-1][j] == a[i][j] && b[i-1][j] == b[i][j] )
                while(1);

and I have wa4, not TL

Did you number the bricks correctly?

I numbered bricks by squares:
xx
yy

or
xy
xy

Maybe it wrong?

Use int instead of char. There can be numbers up to 5000 in the answer.

Thank you! AC)