# LeetCode 1394. Find Lucky Integer in an Array

## 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: 2
Explanation: The only lucky number in the array is 2 because frequency == 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 = 
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).