【Leetcode】H-Index II

题目链接：https://leetcode.com/problems/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:
Expected runtime complexity is in O(log n) and the input is sorted.

思路：

用二分查找法。

算法：

[java] view
plain copy

 





public int hIndex(int[] citations) {  

    int h = 0;  

    int right = citations.length - 1, left = 0, mid = (right - left) / 2 + left;  

    while (right >= left) {  

        if (citations[mid] < citations.length - mid) {  

            left = mid + 1;  

        } else if (citations[mid] >= citations.length - mid) {  

            right = mid - 1;  

            h = citations.length - mid;  

            if (mid - 1 >= 0 && citations[mid - 1] < citations.length - mid + 1)  

                return h;  

        }  

        mid = (right - left) / 2 + left;  

    }  

    return h;  

}