Given an array of numbers, find the 2 elements/numbers from the array that add up to a given sum

findarraysum.js

/*
  eg. [1,2,3,9] Sum = 8, Output = -1 //not found
  [1,2,4,4] Sum = 8, Output = 2,3 //found (return the index of matched elements)
  
  Assumption - input array is sorted
  
  This solution here is the fastest way, which is O(n) - linear time
*/

function findElementsThatAddToASum(arr, sum) {
  var low = 0,
      high = arr.length - 1;
  
  while (low <= high) {
    if(arr[low] + arr[high] === sum) {
      return "Found: " + low + ", " + high; //found the 2 elements that add up to the sum
    } else if(arr[low] + arr[high] < sum) {
      low = low + 1;
    } else {
      high = high - 1;
    }
  }
  
  return -1; //not found
}