Find Lucky Integer in an Array — LeetCode 1394 Python Solution

The problem

Given an array of integers arr, a lucky integer is an integer that has a frequency in the array equal to its value. Return the largest lucky integer in the array.

Example

Input

arr = [2,2,3,4]

Output

2

Explanation

The only lucky number in the array is 2 because frequency[2] == 2.

Python solution

class Solution:
    def findLucky(self, arr: List[int]) -> int:
        cnt = Counter(arr)
        return max((x for x, v in cnt.items() if x == v), default=-1)

Complexity

Pattern: Hash Map

Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 1394. Find Lucky Integer in an Array is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Hash Table and Counting.

The hash map guide has the Python template for the pattern and the 709 LeetCode problems that use it.

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