# H-Index Problem

## Description

LeetCode Problem 274.

Given an array of integers citations where citations[i] is the number of citations a researcher received for their i^th paper, 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.

Example 1:

``````1
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Input: citations = [3,0,6,1,5]
Output: 3
Explanation: [3,0,6,1,5] means the researcher has 5 papers in total and each of them had received 3, 0, 6, 1, 5 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 = [1,3,1]
Output: 1
``````

Constraints:

• n == citations.length
• 1 <= n <= 5000
• 0 <= citations[i] <= 1000

## Sample C++ Code

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class Solution {
public:
int hIndex(vector<int>& citations) {
int len = citations.size();
sort(citations.begin(), citations.end());

if (len == 1)
return (citations == 0) ? 0 : 1;

int left = 0, right = len-1;
int mid;

while (left <= right) {
mid = (left + right) / 2;
if (citations[mid] == (len-mid))
return len-mid;
else if (citations[mid] < (len-mid)) {
left = mid + 1;
} else {
right = mid - 1;
}

}
return len-left;
}
};
``````