1394. Find Lucky Integer in an Array

Problem

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 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

Solution (Java)

class Solution {
    public int findLucky(int[] arr) {
        int[] numbers = new int[501];
        for (int j : arr) {
            numbers[j]++;
        }
        for (int i = 500; i > 0; i--) {
            if (i == numbers[i]) {
                return i;
            }
        }
        return -1;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).