<pre class="shiki github-dark shaku"><code>/** * @param {HTMLElement | null} root * @return {HTMLElement[]} */function flatten(root) { // your code here if(!root) return []; let result = [root]; let i = 0; while(i &lt; result.length) { let node = result[i]; if(node.childNodes &amp;&amp; node.childNodes.length) { result.push(...node.children); } i++; } return result;}</code></pre>

BFS, 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…