5368_lucky_number.py

'''
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(object):
    def findLucky(self, arr):
        """
        :type arr: List[int]
        :rtype: int
        """
        ht = dict()
        for e in arr:
            ht[e] = ht.get(e, 0) + 1
        res = -1
        for k in ht:
            v = ht[k]
            if k == v:
                res = max(res, k)
        return res


s = Solution()
# arr = [2,2,2,3,3]
arr = [2,2,3,4]
res = s.findLucky(arr)
print(res)