# 275. H-Index II

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?

# Solution

Approach 1: Binary search.

# Code (Python)

Approach 1:

# Code (C++)

Approach 1:

class Solution {
public:
    int hIndex(vector<int>& citations) {
        int n = citations.size();
        int lo = 0;
        int hi = n - 1;
        while (lo <= hi)
        {
            int mid = lo + (hi - lo) / 2;
            if (citations[mid] < n - mid)
                lo = mid + 1;
            else if (citations[mid] > n - mid)
                hi = mid - 1;
            else
                return n - mid;
        }
        return n - lo;
    }
};