H-Index II

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

Solution

public class Solution {
   public int hIndex(int[] citations) {
        if (citations == null || citations.length == 0) return 0;

        int size = citations.length;
        int start = 0;
        int end = size - 1;

        while (start <= end) {
            int middle = start + (end - start) / 2;
            if (size - middle > citations[middle]) {
                start = middle + 1;
            } else if (size - middle == citations[middle]) {
                return citations[middle];
            } else {
                end = middle - 1;
            }
        }

        return size - start;
    }
}