1394. Find Lucky Integer in an Array

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Problem

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

Code

class Solution {
    public int findLucky(int[] arr) {
        HashMap<Integer, Integer> map = new HashMap<>();
        for(int num : arr) {
            map.put(num, map.getOrDefault(num, 0) + 1);
        }

        Integer maxKey = -1;
        for(int key : map.keySet()) {
            if(key == map.get(key)) {
                maxKey = Math.max(maxKey, key);
            }
        }

        return maxKey;
    }
}