input: Write a function to find a pair of numbers that add up to a target value from a list.
  assert find_pair([1, 2, 3, 4, 4, 5, 6], 8) == [2, 6]
  assert find_pair([10, 20, 30, 40, 50], 70) == [20, 50]
  assert find_pair([1, 3, 5, 7, 9], 10) == [1, 9]
output: def find_pair(nums, target):
      seen = {}
      for num in nums:
          complement = target - num
          if complement in seen:
              return [complement, num]
          seen[num] = True
      return []