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BJP4 Exercise 17.11: numberNodes

Language/Type: Java binary trees implementing IntTree
Author: Robert Baxter (on 2016/09/08)

Write a method `numberNodes` that changes the data stored in a binary tree, assigning sequential integers starting with `1` to each node so that a pre-order traversal will produce the numbers in order(`1`, `2`, `3`, etc.). For example, given the tree referenced by `tree` below at left, the call of `tree.numberNodes();` would overwrite the existing data assigning the nodes values from `1` to `6` so that a pre-order traversal of the tree would produce `1`, `2`, `3`, `4`, `5`, `6`.

Before Call After Call
```          +---+
| 7 |
+---+
/     \
+---+     +---+
| 3 |     | 9 |
+---+     +---+
/     \         \
+---+     +---+     +---+
| 9 |     | 2 |     | 0 |
+---+     +---+     +---+
```
```          +---+
| 1 |
+---+
/     \
+---+     +---+
| 2 |     | 5 |
+---+     +---+
/     \         \
+---+     +---+     +---+
| 3 |     | 4 |     | 6 |
+---+     +---+     +---+
```

You are not to change the structure of the tree. You are simply changing the values stored in the data fields. Your method should return a count of how many nodes were in the tree.

Assume that you are adding this method to the `IntTree` class as defined below:

```public class IntTree {
private IntTreeNode overallRoot;
...
}
```