1394 - Find Lucky Integer in an Array\.

Easy

Given an array of integers arr, a lucky integer is an integer that has a frequency in the array equal to its value.

Return the largest lucky integer in the array. 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 frequency2 == 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.

Constraints:

• 1 <= arr.length <= 500

• 1 <= arr[i] <= 500