274. H-Index

QUESTION:

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 
Explanation: [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.

Note: If there are several possible values for h, the maximum one is taken as the h-index.

EXPLANATION:

这题目看起来很难，其实就是很难理解，但是如果从wiki的角度来发现的就可以看到。h-index 说的就很清楚：

  1. 首先将数组进行由大到小的排序
  2. 然后找到最后一个f比当前的位置i还要大

SOLUTION:

class Solution {
    public int hIndex(int[] citations) {
        Integer[] ints = new Integer[citations.length];
        for(int i = 0;i<citations.length;i++) ints[i] = new Integer(citations[i]);
        Arrays.sort(ints,Collections.reverseOrder());
        for(int i=0;i<ints.length;++i){
            if(ints[i]<i+1) return i;
        }
        return ints.length;
    }
}
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