275. H-Index II-优快云博客

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.

Follow up:

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?

public class Solution {
    public int hIndex(int[] citations) {
        final int n = citations.length;
        int begin = 0;
        int end = citations.length;

        while (begin < end) {
            final int mid = begin + (end - begin) / 2;
            if (citations[mid] < n - mid) {
                begin = mid + 1;
            } else {
                end = mid;
            }
        }
        return n - begin;
    }
}