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.

题目含义：求出文章索引的H-index值。对于h-index，意思是某个学者有n篇文章，找出最大的h，使得该作者有h篇文章，并且这h篇文章的引用次数都大于等于h。 

思路：降序排列给定数组，从头开始找引用值itations[i]小于等于文章数i的值

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275. H-Index II

 1     public int hIndex(int[] citations) {
 2         Arrays.sort(citations);
 3         int left=0,right=citations.length-1;
 4         while (left<right)
 5         {
 6             int temp = citations[left];
 7             citations[left] = citations[right];
 8             citations[right] = temp;
 9             left++;right--;
10         }
11         for (int i = 0; i < citations.length; ++i) {
12             if (i >= citations[i]) return i;
13         }
14         return citations.length;        
15     }