1394. Find Lucky Integer in an Array⌗

Difficulty: Easy

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

Return a lucky integer in the array. If there are multiple lucky integers return the largest of them. If there is no lucky integer return -1.

Example 1:

Input: arr = [2,2,3,4]
Output: 2
Explanation: The only lucky number in the array is 2 because frequency[2] == 2.

Example 2:

Input: arr = [1,2,2,3,3,3]
Output: 3
Explanation: 1, 2 and 3 are all lucky numbers, return the largest of them.

Example 3:

Input: arr = [2,2,2,3,3]
Output: -1
Explanation: There are no lucky numbers in the array.

Example 4:

Input: arr = [5]
Output: -1

Example 5:

Input: arr = [7,7,7,7,7,7,7]
Output: 7

Constraints:

  • 1 <= arr.length <= 500
  • 1 <= arr[i] <= 500

Solution⌗

Language: Python3

class Solution:
    def findLucky(self, arr: List[int]) -> int:
        res = -1
        for x in arr:
            if(arr.count(x) == x):
                if x > res:
                    res = x
        return res

##Only faster than 6.0% of submission

fast one liner Python

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

class collections.Counter([iterable-or-mapping])

Counter is a dict subclass for counting hashable objects. It is collection where elements are stored as dictionary and their counts are stored as dictionary values