## BJP4 Exercise 14.9: switchPairs

Language/Type: Java Collections Stacks and Queues
Author: Marty Stepp (on 2016/09/08)

Write a method `switchPairs` that takes a stack of integers as a parameter and that switches successive pairs of numbers starting at the bottom of the stack. For example, if the stack initially stores these values:

```bottom [3, 8, 17, 9, 99, 9, 17, 8, 3, 1, 2, 3, 4, 14] top
```

Your method should switch the first pair (3, 8), the second pair (17, 9), the third pair (99, 9), and so on, yielding this sequence:

```bottom [8, 3, 9, 17, 9, 99, 8, 17, 1, 3, 3, 2, 14, 4] top
```

If there are an odd number of values in the stack, the value at the top of the stack is not moved. For example, if the original stack had stored:

```bottom [3, 8, 17, 9, 99, 9, 17, 8, 3, 1, 2, 3, 4, 14, 42] top
```

It would again switch pairs of values, but the value at the top of the stack (42) would not be moved, yielding this sequence:

```bottom [8, 3, 9, 17, 9, 99, 8, 17, 1, 3, 3, 2, 14, 4, 42] top
```

Do not make assumptions about how many elements are in the stack. Use one queue as auxiliary storage.