Leetcode 题目解析之 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."

For example, given citations = 3, 0, 6, 1, 5, which 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, his h-index is 3.

Note: If there are several possible values for h, the maximum one is taken as the h-index.

Hint:

• An easy approach is to sort the array first.
• What are the possible values of h-index?
• A faster approach is to use extra space.

题目描述不清，实际上，H-Index的核心计算方法是：

• 将某作者的所有文章的引用频次按照从大到小的位置排列
• 从前到后，找到最后一个满足条件的位置，其条件为：此位置是数组的第x个，其值为y，必须满足 y >= x;

    public int hIndex(int[] citations) {
        if (citations == null) {
            return 0;
        }
        int h = 0, n = citations.length;
        Arrays.sort(citations);
        for (int i = n - 1; i >= 0; i--) {
            if (citations[i] >= n - i) {
                h = n - i;
            } else {
                break;
            }
        }
        return h;
    }