1394. Find Lucky Integer in an Array

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

Description

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

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