LeetCode-H index II

Follow up for H-Index: What if the citations array is sorted in ascending order? Could you optimize your algorithm?

Analysis:

Binary search: the first non-negative value for ciatations[i]-(len-i)

Solution:

public class Solution {
    public int hIndex(int[] citations) {
        int len = citations.length;
        int start = 0, end = len-1;
        while (start <= end){
            int mid = start + (end-start)/2;
            if (citations[mid] >= len - mid){
                end = mid-1;
            } else {
                start = mid+1;
            }
        }
        return len-start;
    }
}