275. H-Index II

Problem Link

Description

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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 ascending 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.

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.

Solution

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Python3

class Solution:
    def hIndex(self, citations: List[int]) -> int:
        if not citations: return 0
        
        n = len(citations)
        
        beg, end = 0, n - 1
        
        while beg <= end:
            mid = (beg + end)//2
            
            if mid + citations[mid] >= n:
                end = mid - 1
            else:
                beg = mid + 1             
                
        return n - beg