创建一个 C++ 预排序迭代器来为循环提供树节点

Question

I am trying to write a C++ program to supply tree nodes to this loop:

bin_tree<int> *my_tree = ...
for (bin_tree<int>::iterator n = my_tree->begin();
    n != my_tree->end(); ++n)
{
    cout << *n << "\n";
}

The class I have is written in Java, and I would like to translate it into C++, however I am having trouble doing so. This is the class:

class BinTree<T> implements Iterable<T> {
BinTree<T> left;
BinTree<T> right;
T val;
// other methods: insert, delete, lookup, ...

public Iterator<T> iterator()
{
    return new TreeIterator(this);
}
private class TreeIterator implements Iterator<T>
{
    private Stack<BinTree<T>> s = new Stack<BinTree<T>>();
    TreeIterator(BinTree<T> n)
    {
        if (n.val != null) s.push(n);
    }
    public boolean hasNext()
    {
        return !s.empty();
    }
    public T next()
    {
        if (!hasNext()) throw new NoSuchElementException();
        BinTree<T> n = s.pop();
        if (n.right != null) s.push(n.right);
        if (n.left != null) s.push(n.left);
        return n.val;
    }
    public void remove()
    {
        throw new UnsupportedOperationException();
    }
}
}

Any help on how to write this program correctly in C++ would be appreciated, I am not sure how to properly implement the preorder iterator.

Answer 1

If you are trying to create a container that supports iterators I would suggest the following (you probably know all this but it may help you write good C++):

Understand iterators (in your case it may make sense to have bidirectional iterators). Iterators are wrappers to pointers in C++.

Understand the underlying data structure you want (binary tree or binary search tree?).

How should an iterator traverse a tree? (Preorder,inorde,postorder, or level order)

My approach would be to write my own node class/struct. Then write an iterator class that handles the pointer manipulation. If you need to handle allocations a certain way I would write a custom allocator to help too. Finally write your container that uses the other classes. (Modular and separates out functionality in way that is easy to understand in C++)

If you are just looking for the iterator logic and have everything else you need; begin is the first address and can be wrapped as &data [0] for example. End is the last address in similar manner. ++ operator is supported on pointers and will move along linearly towards end. Still will want to figure out moving the tree should work! May even provide multiple ways.

Good luck!