Case #1: 
.......
.......
.......
R......
RB.....
BRB....
RBBR...
Case #2: 
......
R.....
BR....
BRR...
BBBR..
BRBR..
Case #3: 
....
....
BBB.
RRRR
Case #4: 
...
RR.
BBB