You are given an array of integers citations, where each element citations[i] represents the number of citations received for the $i^{th}$ publication of a researcher.

Your task is to find the researcher’s h-index and return the value of $h$.

Note: The h-index is defined as the highest number $h$ such that the given researcher has published at least $h$ papers, each of which has been cited at least $h$ times.

Constraints:

• $n ==$ citations.length

• ...