[LeetCode] H-Index II

This problem is designed specifically to use binary search. In fact, in H-Index, someone has already used this idea (you may refer to this post :-))

The code is as follows.

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