# LeetCode 275. H-Index II – 二分查找（Binary Search）系列题16

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 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:

```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.

``````class Solution:
def hIndex(self, citations: List[int]) -> int:
n = len(citations)
l, r = 0, n - 1

while l <= r:
mid = l + (r - l) // 2
h = n - mid
if citations[mid] >= h:
r = mid - 1
else:
l = mid + 1

return n - l ``````

THE END