## [Leetcode]275. H-Index II

### 题目描述

Given an array of citations sorted in ascending order (each citation is a non-negative integer) of a researcher, write a function to compute the researcher’s h-index.

According to the definition of h-index on Wikipedia: “A scientist has index h if h of his/her N papers have at least h citations each, and the other N − h papers have no more than h citations each.”

### 例子

Input: citations = [0,1,3,5,6] Output: 3 Explanation: [0,1,3,5,6] means the researcher has 5 papers in total and each of them hadreceived 0, 1, 3, 5, 6 citations respectively. Since the researcher has 3 papers with at least 3 citations each and the remaining two with no more than 3 citations each, her h-index is 3. Note:

If there are several possible values for h, the maximum one is taken as the h-index.

### FollowUp

• This is a follow up problem to H-Index, where citations is now guaranteed to be sorted in ascending order.
• Could you solve it in logarithmic time complexity?

### 解题思路

``````class Solution {
public:
int hIndex(vector<int>& citations) {

int left = 0, right = citations.size() - 1;
int result = 0;

while (left <= right) {
int mid = (left + right) / 2;

/// candidate h-index
int h = citations.size() - mid;

if (citations[mid] >= h) {
// current h is a valid h-index, we need to choose the largest one
result = max(result, h);
right = mid - 1;
} else {
left = mid + 1;
}
}

return result;

}
};
``````
• 时间复杂度: O(logN)
• 空间复杂度: O(1)