#### Two Sum

and 4 more contributors
```"""
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 = 2 + 7 = 9,
return [0, 1].
"""
from __future__ import annotations

def two_sum(nums: list[int], target: int) -> list[int]:
"""
>>> two_sum([2, 7, 11, 15], 9)
[0, 1]
>>> two_sum([15, 2, 11, 7], 13)
[1, 2]
>>> two_sum([2, 7, 11, 15], 17)
[0, 3]
>>> two_sum([7, 15, 11, 2], 18)
[0, 2]
>>> two_sum([2, 7, 11, 15], 26)
[2, 3]
>>> two_sum([2, 7, 11, 15], 8)
[]
>>> two_sum([3 * i for i in range(10)], 19)
[]
"""
chk_map: dict[int, int] = {}
for index, val in enumerate(nums):
compl = target - val
if compl in chk_map:
return [chk_map[compl], index]
chk_map[val] = index
return []

if __name__ == "__main__":
import doctest

doctest.testmod()
print(f"{two_sum([2, 7, 11, 15], 9) = }")
```  