H-Index II 二分查找

H-Index II

Follow up for H-Index: What if the

citations

array
is sorted in ascending order? Could you optimize your algorithm?
Hint:

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

class Solution {
public:
//因为是排好序的 然后要求O(logn)，则想到用二分查找
    int hIndex(vector<int>& citations) {
        
        int len=citations.size();
        if(len<=0)
            return 0;
        int mid,left=0,right=len-1;
        while(left<=right)
        {
            mid=left+(right-left)/2;
            if(len-mid==citations[mid])
                return len-mid;
            else if(citations[mid]<len-mid)
                left=mid+1;
            else
                right=mid-1;
        }
        return len-left;
    }
};