275. H-Index II

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

Hint: Expected runtime complexity is in O(log n) and the input is sorted. Binary search.

public class Solution {
    public int hIndex(int[] citations) {
        int left =0; 
        int right = citations.length-1;

        while(left <= right){
            int mid = left + (right-left)/2;
            if(citations[mid] == citations.length - mid) return citations.length - mid; 
            if(citations.length - mid < citations[mid]){
                right = mid-1;
            }else{
                left = mid +1;
            }
        }

        return citations.length - left;
    }
}