Given an array of integers, return indices of the two numbers such that they add up to a specific target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:
---
Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

Note:
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利用字典（hashmap）的快速查找

class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        
        dictionary = {}         # 创建字典，将元素都放进字典中
        for i in range(len(nums)):
            dictionary[nums[i]] = i

        for i in range(len(nums)):
            complement = target - nums[i]
            if complement in dictionary.keys():
                if dictionary.get(complement) != i:
                    x = [i, dictionary.get(complement)]
                    return x