1394. Find Lucky Integer in an Array

Problem Link

Description

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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

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Python3

class Solution:
    def findLucky(self, arr: List[int]) -> int:
        
        C = collections.Counter(arr)
        res = -1
        for c in C:
            if c == C[c]:
                res = max(res, c)
        
        return res

C++

class Solution {
public:
    int findLucky(vector<int>& arr) {
        vector<int> freq(501);
        for (auto x : arr) freq[x]++;
        for (int i = 500; i > 0; i--) {
            if (freq[i] == i) return i;
        }
        return -1;
    }
};