Finds lucky numbers

39th exercise - https://leetcode.com/problems/find-lucky-integer-in-an-array/

luckyNumber.js

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+/*
+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
+*/
+
+//Answer//
+
+/**
+ * @param {number[]} arr
+ * @return {number}
+ */
+var findLucky = function(arr) {
+return Math.max(...arr.filter((x,_,a)=>a.filter(y=>y===x).length===x))===-Infinity?-1:Math.max(...arr.filter((x,_,a)=>a.filter(y=>y===x).length===x))
+};