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Find Lucky Integer in an Array

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

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.

Find Lucky Integer in an Array diagram

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.

Constraints

  • 1 <= arr.length <= 500
  • 1 <= arr[i] <= 500

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