leetcode:（274）H-Index(java)

package LeetCode_HashTable;


/**
 * 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."
 *      Example:
 *          Input: citations = [3,0,6,1,5]
 *          Output: 3
 *          [3,0,6,1,5] 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, her h-index is 3.
 *          （3,0,6,1,5]表示研究人员共有5篇论文，每篇论文分别获得3次，0次，6次，1次5次引用。由于研究人员有3篇论文，每篇论文至少引用3篇，
 *          其余两个每个引用次数不超过3次，她的h指数为3。）
 *  题目大意：
 *      给定研究者的引用数组（每个引用是非负整数），编写一个函数来计算研究者的h指数。
 *      根据维基百科上h-index的定义：“如果他/她的N篇论文中至少有h引文，那么科学家就有索引h，其他的N-h论文每篇都不超过引       数。”
 * 解题思路：
 *      根据给出的数组citations创建一个新的数组array，使新数组的索引代表论文被引用的次数，数组值代表引用次数出现的次数。
 *      然后从新数组的末尾开始向数组的头部开始遍历，在每次遍历时，将数组值累加求和sum,若出现所求和大于数组索引，
 *      则此时的数组索引即为所求的h指数。
 */
public class HIndex_274_1022 {
    public int HIndex(int[] citations) {
        if (citations == null || citations.length == 0) {
            return 0;
        }

        int length = citations.length;
        int[] array = new int[length + 1];
        for (int i = 0; i < length; i++) {
            if (citations[i] >= length) {
                array[length] += 1;
            } else array[citations[i]] += 1;
        }

        int result ; 
        int num = 0;
        for (result = length; result >= 0; result--) {
            num += array[result];
            if (num >= result) {
                return result;
            }
        }
        return 0;
    }

    public static void main(String[] args) {
        int[] array = {3, 0, 6, 1, 5};
        HIndex_274_1022 test = new HIndex_274_1022();
        int result = test.HIndex(array);
        System.out.println(result);
    }
}