**H-Index - Google Top Interview Questions**

### Problem Statement :

In academia, the h-index is a metric used to calculate the impact of a researcher's papers. It is calculated as follows: A researcher has index h if at least h papers have at least h citations each. If there are multiple h satisfying this formula, the maximum is chosen. Given a list of paper citations of a researcher citations, calculate their h-index. Constraints n ≤ 100,000 where n is the length of citations Example 1 Input citations = [4, 3, 0, 1, 5] Output 3 Explanation At least 3 papers have at least 3 citations each: 3, 4, 5. Example 2 Input citations = [4, 4, 0, 1, 5, 9] Output 4 Explanation At least 4 papers have 4 citations each: 4, 4, 5, 9. Example 3 Input citations = [9, 10, 0, 1, 6] Output 3 Explanation At least 3 papers have 3 citations each: 6, 9, 10.

### Solution :

` ````
Solution in C++ :
int solve(vector<int>& citations) {
int h = 0, N = citations.size();
sort(citations.begin(), citations.end());
for (int i = 0; i < N; i++) {
if (citations[i] >= h && N - i >= h) {
h = min(citations[i], N - i);
}
}
return h;
}
```

` ````
Solution in Java :
import java.util.*;
class Solution {
public int solve(int[] citations) {
Arrays.sort(citations);
int n = citations.length;
int hIndex = Integer.MIN_VALUE;
for (int i = 0; i < n; i++) {
int hPapers = n - i;
int hCitations = citations[i];
hIndex = Math.max(hIndex, Math.min(hPapers, hCitations));
}
return hIndex;
}
}
```

` ````
Solution in Python :
class Solution:
def solve(self, citations):
lo, hi = 0, len(citations)
while lo < hi:
mid = (lo + hi + 1) // 2
cnt = 0
for citation in citations:
if citation >= mid:
cnt += 1
if cnt >= mid:
lo = mid
else:
hi = mid - 1
return lo
```

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