Skip to main content

Check If N and Its Double Exist

Problem statement​

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: trueExplanation: N = 10 is the double of M = 5,that is, 10 = 2 * 5.

Example 2:

Input: arr = [7,1,14,11]Output: trueExplanation: N = 14 is the double of M = 7,that is, 14 = 2 * 7.

Example 3:

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

Constraints:

  • 2 <= arr.length <= 500
  • -10^3 <= arr[i] <= 10^3

My solution​

/**
 * @param {number[]} arr
 * @return {boolean}
 */
var checkIfExist = function(arr) {
    const track = new Set();
    for (let i = 0; i < arr.length; i++) {
        const double = arr[i] * 2;
        if (track.has(double) || (arr[i] % 2 === 0 && track.has(arr[i]/2))) {
            return true;
        }
        track.add(arr[i]);
    }
    
    return false;
};