H-Index

Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher’s h-index.
According to the definition of h-index on Wikipedia: “A scientist has index h if h of his/her N papers have at least h citations each, and the other N − h papers have no more than h citations each.”
For example, given citations = [3, 0, 6, 1, 5], which means the researcher has 5 papers in total and each of them had received 3, 0, 6, 1, 5 citations respectively. Since the researcher has 3 papers with at least 3 citations each and the remaining two with no more than 3 citations each, his h-index is 3.
Note: If there are several possible values for h, the maximum one is taken as the h-index.
Hint:
* An easy approach is to sort the array first.
* What are the possible values of h-index?
* A faster approach is to use extra space.

Solution:
1. public class Solution {
2. public int hIndex(int[] citations) {
3. Arrays.sort(citations);
4. 5. int n = citations.length, max = 0;
6. 7. for (int i = 0; i < n; i++)
8. max = Math.max(max, Math.min(citations[i], n - i));
9. 10. return max;
11. }
12. }