function twoSum(arr, targetNum) {
  var i = 0;
  var j = arr.length-1;
  while (i < j){
    if (arr[i] + arr[j] === targetNum) {
      return [i, j];
    } else if (arr[i] + arr[j] > targetNum) {
      j--;
    } else if (arr[i] + arr[j] < targetNum) {
      i++;
    }
  }
  return [-1, -1];
}

var arr = [1, 3, 4, 5, 6, 11, 14]
var targetNum = 27;

twoSum (arr, targetNum);