89. Next Right Sibling

easy  - accepted / - tried

Given a DOM tree and a target element, please return the next right sibling.

Like above, the next right sibling of <button/> is the blue <a/>. Notice that they don't necessarily have the same parent element.

If no right sibling, then return null.

What is time & space cost of your solution ?

What is time & space complexity of your approach?