# 1394. 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] == 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`

找数组中出现次数和值相等中最大的数，没有次数和值相等的元素时返回-1。依题意统计频率后找max。

```python
class Solution:
    def findLucky(self, arr: List[int]) -> int:
        cnt = collections.Counter(arr)
        return max([k for k, v in cnt.items() if k == v] + [-1])
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://hao-fu-1.gitbook.io/oj/hash/tong-ji-pin-lv/1394.-find-lucky-integer-in-an-array.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.