## The challenge

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[] + nums[1] = 2 + 7 = 9, return [,1].

## The solution in Python

```
class Solution:
def twoSum(self, nums: List[int], target: int) -> List[int]:
# keep a hashmap of items found
seen = {}
# loop through the nums, with int and value
for i, v in enumerate(nums):
# set remaining to the target minus the value
remaining = target - v
# check if the new value is in the hashmap
if remaining in seen:
# return it and the index
return [seen[remaining], i]
# otherwise, put it on the map instead
seen[v] = i
# nothing found, return an empty list
return []
```