1394. Find Lucky Integer in an Array

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

Sort first, take the map storage frequency, and then check whether they are equal from large to small, because the title says that if there are multiple numbers, the largest is returned.

class Solution {
    public int findLucky(int[] arr) {
        Arrays.sort(arr);
        Map<Integer, Integer> map = new HashMap();
        for(int i: arr){
            map.put(i, map.getOrDefault(i,0) + 1);
        }
        for(int i = arr.length - 1; i > -1; i--){
            if(map.get(arr[i]) == arr[i]) return arr[i];
        }
        return -1;
    }
}