89. Next Right Sibling

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medium  - 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 ?

Let's try to solve this problem within 15 minutes.