# Question

Formatted question description: https://leetcode.ca/all/275.html

 275	H-Index II

Given an array of citations sorted in ascending order (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 = [0,1,3,5,6]
Output: 3

Explanation: [0,1,3,5,6] means the researcher has 5 papers in total and each of them had
received 0, 1, 3, 5, 6 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.

This is a follow up problem to H-Index, where citations is now guaranteed to be sorted in ascending order.
Could you solve it in logarithmic time complexity?



# Algorithm

First initialize left and right to 0 and len-1, then take the middle value mid, compare citations[mid] with len-mid,

• If the former is big, right moves before mid
• On the contrary, right moves after mid The loop condition is left<=right, and finally returns len-left.

Java