兄弟连PHP教程随堂笔记，LeetCode:H-Index ，订阅走一波，值得收藏！
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.
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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.
Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.
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(M) H-Index II
思路：
首先阐述一个事实：h-index不超过L（即h-index <= L）；当h-index == L时，citations所有值都不小于L；
创建一个counts数组，存储citation == index（index<L时），当index>=L时，存入counts[L]；
如有数组citations = [3,0,7,1,5]，L = 5；
创建counts[L+1]数组，存储方式为：
if(citaion == index) counts[index]++;
if(citation >= L) counts[L]++;
最后，从右向左遍历counts，并用ans变量记录个数；当ans>=i时，即得解。
Java code:
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