# [275. H-Index II](https://leetcode.com/problems/h-index-ii/)
# 思路
这题实际上是[274. H-Index](https://leetcode.com/problems/h-index/)的简化版，274题引用列表没有排好序此题已经排序了。
所以会做274题的话此题肯定没问题，[274题思路二](https://github.com/ShusenTang/LeetCode/blob/master/solutions/274.%20H-Index.md)其实就和此题的解法类似，复杂度为O(logn)，这里不再赘述。

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