My code:

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

用 Binary search 找最接近target并且 >= target 的 那个index
果然还是很常用的算法，一定要记住。

Anyway, Good luck, Richardo! — 09/21/2016