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."Example: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, her h-index is 3.Note: If there are several possible values for h, the maximum one is taken as the h-index.

1、将其发表的所有SCI论文按被引次数从高到低排序；2、从前往后查找排序后的列表，直到某篇论文的序号大于该论文被引次数。所得序号减一即为H指数。

class Solution {    public int hIndex(int[] citations) {        int size = citations.length;        if(size<=0)            return 0;        Arrays.sort(citations);        int count = 0;        for(int i = size-1;i>=0;i--){            if(count>=citations[i])                return Math.max(count,citations[i]);            count++;        }        return count;    }}