1394. Find Lucky Integer in an Array-找出数组中的幸运数

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 in python:

class Solution:
    def findLucky(self, arr: List[int]) -> int:
        adic = dict()
        for item in arr:
            if item not in adic.keys():
                adic[item] = 1
            else:
                adic[item] += 1
        result = -1
        for key, value in adic.items():
            if key == value and value > result:
                result = value
        return result