H-Index-II.java

/*
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?
*/

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