O(nlogn) time and O(1) space using Sorting.

Author: 149ps

274. H-Index/274. H-Index.py

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+"""
+Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher's h-index.
+
+According to the definition of h-index on Wikipedia: "A scientist has index h if h of his/her N papers have at least h citations each, and the other N − h papers have no more than h citations each."
+
+Example:
+
+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, her h-index is 3.
+Note: If there are several possible values for h, the maximum one is taken as the h-index.
+"""
+class Solution:
+    def hIndex(self, citations: List[int]) -> int:
+        citations.sort(reverse = True)
+        result = 0
+        for i in range(len(citations)):
+            if citations[i] - 1 >= i:
+                result += 1
+        return result