LeetCode 1394. Find Lucky Integer in an Array

The Problem

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.

Examples

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

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 = 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;
};

LeetCode 1394. Find Lucky Integer in an Array

The Problem

My Solution