This may be fine if our input is small, but this grows quite fast, as every additional element in the input will require a number of operations equivalent to the input length. The time complexity would be O(n^2). A better methodology is to use a data structure-- specifically, a hash map.

Using a hash map, we can set up a separate tracker, where the keys represent the difference between the goal and a number at an index.

The above is a visual of a hash map data structure.

So if we had an array of numbers [1, 3, 5], and the target/goal was 4, here's the example hash map that we'd generate:

xxxxxxxxxx

const arr = [1, 3, 5];

const goal = 4;

​

const hash = {

  3: 0,  // 4 - 1 = 3 at index 0

  1: 1,   // 4 - 3 = 1 at index 1

  -1: 2  // 4 - 5 = -1 at index 2

}

​

console.log(hash);