H-Index II

Follow up for H-Index: What if the citations array is sorted in ascending order? Could you optimize your algorithm?

要求用二分法做。

 1 public class Solution {
 2     public int hIndex(int[] citations) 
 3     {
 4  
 5         if(citations.length==0)return 0;
 6         int left=0;
 7         int right=citations.length-1;
 8         int mid=0;
 9         while(left+1<right)
10         {
11             mid=(left+right)/2;
12             if(citations[mid]<citations.length-mid)
13             {
14                 left=mid;
15             }
16             else //citations[mid]>=right-mid
17             {
18                 right=mid;
19             }
20         }
21         if(citations[left]>=citations.length-left) return citations.length-left;
22         if(citations[right]>=citations.length-right) return citations.length-right;
23         return 0;
24     }
25 }