Q38

Let $\mathrm{S} 1$ and $\mathrm{S} 2$ be two stacks. $\mathrm{S} 1$ has capacity of $4$ elements. $\mathrm{S} 2$ has capacity of $2$ elements. $\text{S1}$ already has $4$ elements: $100,200,300$, and $400$, whereas $\text{S2}$ is empty, as shown below.

$$\underset{\Large{\text{Stack S1}}}{\begin{array}{|l|} \hline 400\text{(Top)} \\\hline 300 \\\hline 200 \\\hline 100 \\\hline \end{array}}\quad \qquad \underset{\Large{\text{Stack S2}}}{\begin{array}{|l|} \hline &&& \\\hline &&& \\\hline \end{array}}$$

Only the following three operations are available: PushToS2: Pop the top element from S1 and push it on S2. PushToS1: Pop the top element from S2 and push it on S1. GenerateOutput: Pop the top element from S1 and output it to the user. Note that the pop operation is not allowed on an empty stack and the push operation is not allowed on a full stack. Which of the following output sequences can be generated by using the above operations?