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一、题目

Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper and citations is sorted in ascending order, return the researcher’s h-index.

According to the definition of h-index on Wikipedia: The h-index is defined as the maximum value of h such that the given researcher has published at least h papers that have each been cited at least h times.

You must write an algorithm that runs in logarithmic time.

Example 1:

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 had received 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, their h-index is 3.
Example 2:

Input: citations = [1,2,100]
Output: 2

Constraints:

n == citations.length
1 <= n <= 105
0 <= citations[i] <= 1000
citations is sorted in ascending order.

二、题解

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