Solution.java

import java.util.Arrays;

/**
 * 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.
 */

public class Solution {
    public int hIndex(int[] citations) {
        Integer[] newArray = new Integer[citations.length];
        for (int i = 0; i < citations.length ; i ++) {
            newArray[i] = Integer.valueOf(citations[i]);
        }
        Arrays.sort(newArray, Collections.reverseOrder());
        
        for (int i = newArray.length - 1 ; i >= 0 ; i--) {
            if (newArray[i] >= (i+1) && (i == newArray.length - 1 || newArray[i+1] <= (i+1))) {
                return (i+1);
            }
        }
        
        return 0;
    }
}