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Decode the Coding Interview in Kotlin: Real-World Examples

Feature #1: Traversing DOM Tree

Explore how to traverse an n-ary DOM tree structure using Breadth First Search, capturing each level's nodes left to right. Understand the implementation using queues, the process of level order traversal, and the associated time and space complexities. This lesson prepares you to handle web scraping tasks involving HTML tree traversal effectively.

We'll cover the following...

Description

First, we need to figure out a way to traverse the DOM structure that we obtain from a single web page. The HTML can be represented in a tree structure where the children of the HTML tag become the children of a node in the tree. Each level of the tree can have any number of nodes depending upon the number of nested HTML tags. We need to traverse the nodes in the tree level by level, starting at the root node.

<body>

  <nav>

    <a>About</a>

  </nav>

  <p>Paragraph</p>

</body>
DOM Tree
DOM Tree

We’ll be provided with a root node of an n-ary tree. The root node in our case will be the body tag. This root node will have the complete web page nested within its children. We have to return the values of each levels’ nodes from left to right in separate subarrays. This way we can separately analyze their content for further data processing.

Let’s try to understand this better with an illustration:

Solution

Since we need to traverse all the nodes of each level before moving onto the next level, we can use the Breadth First Search (BFS) technique to solve this problem. We can use a queue to efficiently traverse in BFS ...