275、H-Index II

题目：

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

Hint:

1. Expected runtime complexity is in O(log n) and the input is sorted.

解题思路：

很明显，此题要考虑使用二分查找。但对于具体做的方法还是不太明白，希望以后能弄懂。

c++版本：

class Solution {public:    int hIndex(vector<int>& citations) {        int n=citations.size(),lo=0,hi=n-1;        while(lo<=hi)        {            int mid = (lo+hi)>>1;            if(citations[mid]==n-mid)return n-mid;            else if(citations[mid]>n-mid)hi=mid-1;            else                lo=mid+1;        }        return n-lo;    }};