LeetCode Challenge #1394. 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.

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
Video Solution
Java Solution

class Solution {
public int findLucky(int[] arr) {
HashMap<Integer,Integer> hm = new HashMap<>();

for(int i=0;i<arr.length;i++){
int ele = arr[i];

if(hm.containsKey(ele)==true){
hm.put(ele,hm.get(ele)+1);
}else{
hm.put(ele,1);
}
}

int ans = -1 ;
for(int key : hm.keySet()){
if(hm.get(key)==key){
ans = Math.max(ans,key);
}
}

return ans ;
}
}