# Which Data Structure Is Used in Level Order Traversal of the Binary Tree?

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Heather Bennett

When it comes to traversing a binary tree, one common method is the level order traversal. This traversal technique visits all the nodes of a binary tree level by level, from left to right.

But what data structure is used to achieve this? Let’s explore the options.

## The Queue Data Structure

In order to perform a level order traversal of a binary tree, we need a data structure that allows us to visit the nodes in the required order. The queue data structure fits this requirement perfectly.

A queue follows the FIFO (First-In-First-Out) principle, which means that elements are inserted at the back and removed from the front. This behavior aligns well with our goal of visiting nodes in a specific order.

## How Does It Work?

To perform a level order traversal using a queue, we start by enqueuing (inserting) the root node of the binary tree into the queue. Then, we enter into a loop where we continue until the queue becomes empty.

### Inside the Loop:

• We dequeue (remove) an element from the front of the queue and visit its value.
• If there is a left child for this dequeued node, we enqueue it into the queue.
• If there is a right child for this dequeued node, we enqueue it into the queue as well.

This process continues until all nodes have been visited, ensuring that each level is traversed before moving on to the next level. The use of a queue guarantees that elements are processed in their proper order.

## An Example:

Let’s consider an example to illustrate how level order traversal works using a queue. Assume we have the following binary tree:

```          1
/   \
2     3
/ \   / \
4   5 6   7
```

To traverse this tree in level order, we start with the root node (1) and enqueue it into the queue. Then, we enter the loop and dequeue (visit) the front element, which is 1. We enqueue its children, 2 and 3.

Now, the queue contains [2, 3]. Next, we dequeue 2 from the front of the queue and enqueue its children, which are 4 and 5. The queue becomes [3, 4, 5].

We continue this process until all nodes have been visited. The final order of visiting the nodes in level order will be: 1 -> 2 -> 3 -> 4 -> 5 ->6 ->7.

## Conclusion

The level order traversal of a binary tree is an essential technique that allows us to visit all nodes in their respective levels. To achieve this traversal efficiently and accurately, we utilize the queue data structure.

By using a queue to store nodes temporarily during traversal, we can ensure that each level is visited before moving on to the next. This approach guarantees that nodes are processed in their proper order and provides an effective solution for level order traversal.