[LeetCode]H-Index II

H-Index II

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

二分查找，时间复杂度O(logn)。

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