LeetCode H-Index

 1 public class Solution {
 2     public int hIndex(int[] citations) {
 3         /*
 4         //Method 1
 5         if(citations == null || citations.length == 0){
 6             return 0;
 7         }
 8         Arrays.sort(citations);
 9         int res = 0;
10         for(int i = citations.length-1; i>=0; i--){
11             if(citations[i] >= citations.length-i){
12                 res = citations.length-i;
13             }
14         }
15         return res;
16         */
17         
18         //Method 2
19         if(citations == null || citations.length == 0){
20             return 0;
21         }
22         int len = citations.length;
23         //count 数组储存了被引用 i 遍的文章有几个，i是count的index
24         int [] count = new int[len+1];
25         for(int i = citations.length - 1; i>=0; i--){
26             if(citations[i]>=citations.length){
27                 count[len]++;
28             }else{
29                 count[citations[i]]++;
30             }
31         }
32         //total 计数总共有几篇文章引用大于等于i次，i是count 的index
33         int total = 0;
34         for(int i = len; i>=0; i--){
35             total += count[i];
36             if(total>=i){ //有三篇文章引用大于等于三次
37                 return i;
38             }
39         }
40         return 0;
41     }
42 }