double.js

//  Check If N and Its Double Exist

// Given an array arr of integers, check if there exists two integers N and M such that N is the double of M ( i.e. N = 2 * M).

// More formally check if there exists two indices i and j such that :

// i != j
// 0 <= i, j < arr.length
// arr[i] == 2 * arr[j]
 

// Example 1:

// Input: arr = [10,2,5,3]
// Output: true
// Explanation: N = 10 is the double of M = 5,that is, 10 = 2 * 5.
// Example 2:

// Input: arr = [7,1,14,11]
// Output: true
// Explanation: N = 14 is the double of M = 7,that is, 14 = 2 * 7.
// Example 3:

// Input: arr = [3,1,7,11]
// Output: false
// Explanation: In this case does not exist N and M, such that N = 2 * M.

var checkIfExist = function(arr) {
    return arr.filter(num => arr.includes(num * 2 || num/2))
};