Find Lucky Integer in an Array

main.md

Question

Approach

I first count how many times each number appears in the array. I use a frequency map (like Python's Counter) to make this easier. Then, I go through each number and check if its frequency is equal to the number itself. If it is, I consider it a "lucky" number. While doing this, I keep track of the largest such lucky number I find. If I don't find any number that satisfies the condition, I return -1; otherwise, I return the largest lucky number found.

Implementation

class Solution:
    def findLucky(self, arr: List[int]) -> int:
        freq = Counter(arr)
        result = -1
        for num, count in freq.items():
            if num == count:
                result = max(result, num)
        return result

Complexities

• Time: O(n)
• Space: O(n)