## Description

https://leetcode.com/problems/find-lucky-integer-in-an-array/

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:2Explanation:The only lucky number in the array is 2 because frequency[2] == 2.

**Example 2:**

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

**Example 3:**

Input:arr = [2,2,2,3,3]Output:-1Explanation: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`

## Explanation

Just check if the element’s value equals to its count.

## Python Solution

```
class Solution:
def findLucky(self, arr: List[int]) -> int:
counter = {}
for num in arr:
counter[num] = counter.get(num, 0) + 1
lucky = -1
for key, value in counter.items():
if key == value and key > lucky:
lucky = value
return lucky
```

- Time Complexity: O(N).
- Space Complexity: O(N).