# 1394. Find Lucky Integer in an Array

## The Problem

Link to original problem on Leetcode.

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.


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 = 
Output: -1


Example 5:

Input: arr = [7,7,7,7,7,7,7]
Output: 7


Constraints:

• 1 <= arr.length <= 500
• 1 <= arr[i] <= 500

## My Solution

This solution creates a Map of the integer values in arr along with their count. It then iterates over the Map, comparing keys and values for equality. An initial result of -1 is then replaced if a lucky integer is found, and any larger lucky integer will in turn replace a smaller one. This takes $$O(n)$$ time.

const findLucky = function(arr) {    const integers = new Map();    let result = -1;    arr.forEach(i => {        if (!integers.has(i)) {            integers.set(i, 1);        } else {            integers.set(i, 1 + integers.get(i));        }    });    for ([key, value] of integers) {        if (key === value && key > result) {            result = key;        }    }    return result;};