## Problem Statement

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].

**Solution:**

class Solution:
def twoSum(self, nums: List[int], target: int) -> List[int]:
if not nums: return nums
complement = {}
for i in range(len(nums)):
if nums[i] in complement:
return [complement[nums[i]], i]
complement[target-nums[i]] = i