【Leetcode】H-Index

题目链接：https://leetcode.com/problems/h-index/ 题目：

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

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:

1. An easy approach is to sort the array first.
2. What are the possible values of h-index?
3. A faster approach is to use extra space.

思路：

横坐标是数组下标，纵坐标是该论文的引用数。所以求的是最靠近y>=x的横坐标，即citations.length-j。

算法：

        
1. public int hIndex(int[] citations) {  
2.     Arrays.sort(citations);  
3. int h=0;  
4. for (int i = citations.length - 1; i >= 0; i--) {  
5. if (citations[i] >= citations.length - i)//citations.length - i指引用大于citations[i]的paper数目  
6.             h = citations.length - i;  
7.     }  
8. return h;  
9. }