《leetcode》:H-Index

题目

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.

思路

借助一个额外的空间tempArr(长度为N+1)来保存数组中各数字出现的次数。tempArr[N]中保存所有大于等于N的数的次数。然后从N—>1开始统计，只要在N篇paper中至少有h篇论文大于等于h，则才返回h。

实现代码如下：

    //在N篇paper中至少有h篇论文大于等于h，则才返回h。N篇paper最大值返回N    public int hIndex(int[] citations) {        if(citations==null||citations.length==0){            return 0;        }        int len = citations.length;        int[] tempArr = new int[len+1];         for(int i=0;i<len;i++){            if(citations[i]>=len){                tempArr[len]++;            }            else{                tempArr[citations[i]]++;            }        }        int totalNum = 0;        for(int i=len;i>=0;i--){            totalNum +=tempArr[i];            if(totalNum>=i){                return i;            }        }        return 0;    }