<pre class="shiki github-dark shaku"><code>/** To implement the flatten function, we can employ BFS algorithm to convert this given DOM tree into a one-dimensional array in a layer-by-layer order. We can start with a queue that has the root element, and initialize a result array. Then, adding the edge cases: if the root is null just return an empty array. Basically, we use a while loop to iterate through the queue, while the queue is not empty, remove the first element, add it to the result array. After that, repeat the process untill all the children of the current node have been processed. Last, return the result. The time complexity of the flattenDOM function is O(n), where n is the number of nodes in the DOM tree. */function flatten(root) { const res = []; const queue = [root]; if(!root) return res; while(queue.length &gt; 0) { const cur = queue.shift(); res.push(cur); for(let i = 0; i &lt; cur.children.length; i++) { queue.push(cur.children[i]) } } return res;}</code></pre>

O(n)

Amazon

Given a DOM tree, flatten it into an one dimensional array, in the order of layer by layer, like below. [https://cdn.bfe.dev/bfe/img/ykqFdOIOaXFyn2uZ8…