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.
[分析]
扫描一遍citations,使用一个额外数组count[]计数每个引用数的文章数量,引用数大于N(文章总数)的视作N。然后从后往前扫描count[],同时累加已扫描部分记为sum,sum表示引用数>=i的文章总数,因为count[]是从后往前扫描,发现的第一个i即为所求的h-index。
public class Solution { public int hIndex(int[] citations) { if (citations == null || citations.length == 0) return 0; int N = citations.length; int[] count = new int[N + 1]; // count[i] means number of articles which citations >= i for (int i = 0; i < N; i++) { if (citations[i] > N) count[N] += 1; else count[citations[i]] += 1; } int sum = 0; for (int i = N; i >= 0; i--) { sum += count[i]; if (sum >= i) return i; } return 0; } }