main.go

// Source: https://leetcode.com/problems/find-lucky-integer-in-an-array
// Title: Find Lucky Integer in an Array
// Difficulty: Easy
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// 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`
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package main

func findLucky(arr []int) int {
	freqs := make(map[int]int, len(arr))

	for _, num := range arr {
		freqs[num]++
	}

	ans := -1
	for num, freq := range freqs {
		if num == freq {
			ans = max(ans, num)
		}
	}

	return ans
}