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。

public class Solution {
    public int hIndex(int[] citations) 
    {
 
        if(citations.length==0)return 0;
        int left=0;
        int right=citations.length-1;
        int mid=0;
        while(left+1<right)
        {
            mid=(left+right)/2;
            if(citations[mid]<citations.length-mid)
            {
                left=mid;
            }
            else //citations[mid]>=right-mid
            {
                right=mid;
            }
        }
        if(citations[left]>=citations.length-left) return citations.length-left;
        if(citations[right]>=citations.length-right) return citations.length-right;
        return 0;
    }
}