Traversal of Binary Search Tree via loop instead of Recursion

Question

Does anyone know how to traverse a binary search tree using loops instead of recursion?

I have the recursive method

public static int countMatches(BinaryNodeInterface<Integer> tree, Integer key)
{
    int matches = 0;
    if (tree != null)
    {
        if (tree.getData().equals(key))
            matches++;
        matches += countMatches(tree.getLeftChild(), key);
        matches += countMatches(tree.getRightChild(), key);
    }
    return matches;
}

PLEASE indent your code. I can't really look at until it's indented... — Alex K
– Alex K, Commented Dec 4, 2014 at 2:50

Eric · Accepted Answer · 2014-12-04 03:03:41Z

1

You can use do a level order traversal using a queue

public static int countMatches(BinaryNodeInterface<Integer> tree, Integer key)
{
    int matches = 0;
    if (tree == null) return 0;
    Queue<BinaryTreeNodeInterface<Integer>> queue = new LinkedList<BinaryTreeNodeInterface<Integer>>();
    queue.add(tree);
    while (!queue.isEmpty()) {
        BinaryTreeNodeInterface<Integer> current = queue.remove();
        if (current.getData().equals(key)) 
            matches++;
        if (current.getLeftChild() != null)
            queue.add(current.getLeftChild());
        if (current.getRightChild() != null)
            queue.add(current.getRightChild());
    }

    return matches;
}

answered Dec 4, 2014 at 3:03

Eric

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Comments

Archival · Accepted Answer · 2014-12-04 03:04:20Z

0

A simple approach would be to use a List that runs through it either dept of breadth first.

public static int countMatches(BinaryNodeInterface<Integer> tree, Integer key)
{
    ArrayList<Node> open = new ArrayList<Node>();
    open.add(tree.getRoot());
    int matches = 0;
    while(!open.isEmpty())
    {
        if(open.get(0).hasLeft())
            open.add(open.get(0).getLeftChild());
        if(open.get(0).hasRight())
            open.add(open.get(0).getRightChild());
        if(open.get(0).equals(key))
            ++matches;

        open.remove(0);
    }
    return matches;
}

This is probably not the most efficient way of doing it but it should work for what your asking. This one works depth first but it shouldn't be too hard for you to change it to breadth first if you need.

answered Dec 4, 2014 at 3:04

Archival

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1 Comment

Archival Over a year ago

Actually Eric's is probably a better alternative since using a Que over an array list is probably easier to organise

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