python3

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:

        map = {}
        for i in range(len(nums)):
            complement = target - nums[i]
            if complement in map: #如果当前值的互补值已经存在字典中
                return [map[complement],i] #那么返回当前值和互补值的下标
            map[nums[i]] = i #将当前的值存为key，下标存为value