# H-Index II Problem

## Description

LeetCode Problem 275.

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

According to the definition of h-index on Wikipedia: A scientist has an index h if h of their n papers have at least h citations each, and the other n − h papers have no more than h citations each.

If there are several possible values for h, the maximum one is taken as the h-index. You must write an algorithm that runs in logarithmic time.

Example 1:

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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:

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

Constraints:

- n == citations.length
- 1 <= n <= 10^5
- 0 <= citations[i] <= 1000
- citations is sorted in ascending order.

## Sample C++ Code

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