# enumerate
class Solution:
  def twoSum(self, nums: List[int], target: int) -> List[int]:
    # 建立快取 key 為數值差值，Value 為 index
    cache: dict = dict()
    # 遍歷 nums
    for k,v in enumerate(nums):
      # 找到差值
      diff:int = target - v
      # 假如 v 在 cache 中，則回傳
      if v in cache: return [k, cache[v]]
      # 紀錄當前差值與索引
      cache[diff] = k
    # 回傳空 List
    return []