H-Index II — LeetCode 275 Python Solution

The problem

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 non-descending 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.

Example

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.

Python solution

class Solution:
    def hIndex(self, citations: List[int]) -> int:
        n = len(citations)
        left, right = 0, n
        while left < right:
            mid = (left + right + 1) >> 1
            if citations[n - mid] >= mid:
                left = mid
            else:
                right = mid - 1
        return left

Complexity

Pattern: Monotonic Stack

Answer "what is the next greater element" for every position in one pass. LeetCode 275. H-Index II is filed here because the reference solution below belongs to the algorithm family this hub collects, even though its LeetCode tags point elsewhere.

The monotonic stack guide has the Python template for the pattern and the 225 LeetCode problems that use it.

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