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
class Solution:
    def findLucky(self, arr: List[int]) -> int:
        book={}.fromkeys(set(arr))
        for key in list(book.keys()):
            book[key]=arr.count(key)
        result=-1
        for key,value in list(book.items()):
            if key==value:
                result=max(result,key)
        return result
                
        

class Solution:
    def findLucky(self, arr: List[int]) -> int:
        book={}.fromkeys(set(arr))
        for key in list(book.keys()):
            book[key]=arr.count(key)
        result=-1
        for key,value in list(book.items()):
            if key==value:
                result=max(result,key)
        return result
                
        
