Asked by Google

The h-index is a metric used to measure the impact and productivity of a scientist or researcher.

A scientist has index h if h of their N papers have at least h citations each, and the other N - h papers have no more than h citations each. If there are multiple possible values for h, the maximum value is used.

Given an array of natural numbers, with each value representing the number of citations of a researcher's paper, return the h-index of that researcher.

For example, if the array was:

[4, 0, 0, 2, 3]

This means the researcher has 5 papers with 4, 1, 0, 2, and 3 citations respectively. The h-index for this researcher is 2, since they have 2 papers with at least 2 citations and the remaining 3 papers have no more than 2 citations.