Question

I have just made a queue class and I now have to use it to do this.

Write a c++ program to generate all strings using A,B,and C as the letters.

The strings must be generated in the following order:
A
B
C
AA
AB
AC
BA
BB
BC
CA
CB
CC
AAA
AAB
AAC
ABA
ABB
ABC
ACA
ACB
ACC
etc.

It’s supposed to do this until my queue overflows.

Now, I simply don’t understand the algorithm the teacher suggested using, which is this.

Start with A and B and C in the queue.
“Remove it Display it then Add Add Add ”

The add add add thing throws me off, how does it accomplish getting these letters in this particular order?

Answer 1

Let our behavior be:

For any token X, add XA, XB, and XC to the queue.

Our flow will be something like:

Start with a Queue
A B C

Pop (and display) off A
B C

Behave on token: "A"
  add AA
  add AB
  add AC
B C AA AB AC

Pop (and display) off B
C AA AB AC
  add BA
  add BB
  add BC
C AA AB AC BA BB BC

If we pretend our function is

main() {
    Queue q;
    q.add("A");
    q.add("B");
    q.add("C");

    while(true) {
        process(q.pop());
    }
}

process(String x, Queue q) {
    display x;
    q.add(x + "A");
    q.add(x + "B");
    q.add(x + "C");
}

Get it now?