README_EN.md

1394. Find Lucky Integer in an Array

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Description

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

Solutions

Python3

class Solution:
    def findLucky(self, arr: List[int]) -> int:
        counter = collections.Counter(arr)
        ans = -1
        for num, n in counter.items():
            if num == n and ans < num:
                ans = num
        return ans

Java

class Solution {
    public int findLucky(int[] arr) {
        Map<Integer, Integer> mp = new HashMap<>();
        for (int num : arr) {
            mp.put(num, mp.getOrDefault(num, 0) + 1);
        }
        int ans = -1;
        for (int num : arr) {
            if (num == mp.get(num) && ans < num) {
                ans = num;
            }
        }
        return ans;
    }
}

C++

class Solution {
public:
    int findLucky(vector<int>& arr) {
        int n = 510;
        vector<int> counter(n);
        for (int e : arr) ++counter[e];
        int ans = -1;
        for (int i = 1; i < n; ++i)
        {
            if (i == counter[i] && ans < i) ans = i;
        }
        return ans;
    }
};

Go

func findLucky(arr []int) int {
    n := 510
    counter := make([]int, n)
    for _, e := range arr {
        counter[e]++
    }
    ans := -1
    for i := 1; i < n; i++ {
        if i == counter[i] && ans < i {
            ans = i
        }
    }
    return ans
}

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