_274.java

package com.fishercoder.solutions;

import java.util.Arrays;

/**
 * 274. 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.
 */
public class _274 {
    public static class Solution1 {
        public int hIndex(int[] citations) {
            if (citations == null || citations.length == 0) {
                return 0;
            }

            Arrays.sort(citations);
            for (int i = 0; i < citations.length; i++) {
                if (citations[i] >= citations.length - i) {
                    return citations.length - i;
                }
            }
            return 0;
        }
    }
}