【LeetCode】274.H-Index(Medium)解题报告

【LeetCode】274.H-Index(Medium)解题报告

题目地址：https://leetcode.com/problems/h-index/description/
题目描述：

  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.

Solution1:

//time : O(nlogn)
//space : O(1)
//3 0 6 1 5
//0 1 3 5 6
class Solution {
    public int hIndex(int[] citations) {
        Arrays.sort(citations);
        int res = 0;
        while(res < citations.length && citations[citations.length - 1 - res]>res){
            res++;
        }
        return res;
    }
}

Solution2:

//time : O(n)
//space : O(n)
//100 0 1 98 4
//helper: 0 1 0 0 1 2
//res = 3
class Solution {
    public int hIndex(int[] citations) {
        //helper表示文章被引用了helper[i]次
        int[] helper = new int[citations.length+1];
        for(int i=0 ; i1;
        }
        int sum = 0;
        for(int i=citations.length ; i>0 ; i--){
            sum += helper[i];
            if(sum >= i){
                return i;
            }
        }
        return 0;
    }
}

Date：2018年2月20日