//constant space, n log n + n time
def twoSumConstSpace(list: Array[Int], k: Int): Option[Result] = {
  util.Arrays.sort(list)
  var i = 0
  var j = list.length - 1
  while (i < j) {
    val sum = list(i) + list(j)
    if (sum == k) {
      return Some(Result(i, j))
    } else if (sum < k) {
      i += 1
    } else {
      j -= 1
    }
  }
  None
}

case class Result (
    aIdx: Int,
    bIdx: Int
)