0274. H-Index

https://leetcode.com/problems/h-index

Description

Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper, return compute the researcher's h-index.

According to the definition of h-index on Wikipedia: A scientist has an 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 several possible values for h, the maximum one is taken as the h-index.

Example 1:

**Input:** citations = [3,0,6,1,5]
**Output:** 3
**Explanation:** [3,0,6,1,5] 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, their h-index is 3.

Example 2:

**Input:** citations = [1,3,1]
**Output:** 1

Constraints:

• n == citations.length

• 1 <= n <= 5000

• 0 <= citations[i] <= 1000

ac1: sorting

O(NlogN) complexity Key: understand the definition of h-index

class Solution {
    public int hIndex(int[] citations) {
        Arrays.sort(citations);

        int n = citations.length;
        int h = 0;
        for (int i = 1; i <= n; i++) {
            if ( citations[n-i] >= i && (i == n || citations[n-i-1] <= i)){
                h = i;
            }
        }

        return h;
    }
}