[leetcode-274]H-Index(java)

问题描述：
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.

分析：这道题的思路是先对数组排序，然后从后向前遍历，维护一个count变量，当count值大于或等于现在的值时，就可以返回了。如果到最后退出循环时，仍未返回，那表示数组中的数都大于count，那么就返回count。因为此时有0个数小于count，有count数大于count。

代码如下：360ms

public class Solution {
    public int hIndex(int[] citations) {
        int size = citations.length;
        if(size<=0)
            return 0;
        Arrays.sort(citations);
        int count = 0;

        for(int i = size-1;i>=0;i--){
            if(count>=citations[i])
                return Math.max(count,citations[i]);
            count++;
        }
        return count;
    }
}