Initial seat pattern:

$1$ A B C D

$2$ A $B$ B $C$ C $D$

$3$ A $B$ B $C$ C $D$

$4$ A B $C$ C $D$

$5$ A B C C D

Enter seat row $(1-5)$ and column $($A$-$D$)$ or

$\text{'}Q\text{'}$ to quit: $3$B

Seat $3$B assigned.

$1$ A B C C D

$2$ A $B$ B $C$ C $D$

$4$ A $B$ B $C$ C $D$

$5$ A B $C$ C $D$

Enter seat row $(1-5)$ and column $($A$-$D$)$ or

$\text{'}Q\text{'}$ to quit: $2C$

Seat $2$C assigned. $1$ A B C D

$2$ A B X D

$3ACD$

$4$ A $B$ B $C$ C $D$

$5$ A B $C$ C $D$

Enter seat row $(1-5)$ and column $($A$-$D$)$ or

$\text{'}Q\text{'}$ to quit: $4A$

Seat $4$A assigned.

$1$ A B C D

$2$ A $B$ B $xx$

$3$AxCCD

$4$ X B C C D

$5$ A B C C D

Enter seat row $(1-5)$ and column $($A$-$D$)$ or

$\text{'}Q\text{'}$ to quit: $6$D

Invalid seat selection.

Please try again. Enter seat row $(1-5)$ and

column $($A$-$D$)$ or $\text{'}Q\text{'}$ to quit: $Q$