day-133.cpp

/*
  H-Index


Given an array of citations (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 = [3,0,6,1,5]
Output: 3
Explanation: [3,0,6,1,5] means the researcher has 5 papers in total and each of
them had received 3, 0, 6, 1, 5 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.
*/

// Sorted + Binary Search to solve the problem
class Solution {
   public:
    int hIndex(vector<int>& citations) {
        sort(citations.begin(), citations.end());
        int N = citations.size();
        int start = 0;
        int end = N - 1;

        while (start <= end) {
            int mid = start + (end - start) / 2;
            if (citations[mid] < (N - mid)) {
                start = mid + 1;
            } else {
                end = mid - 1;
            }
        }

        return N - start;
    }
};