"""

Two Sum

Given an array of integers and a target sum, return the indices of the two

numbers that add up to the target.

Reference: https://leetcode.com/problems/two-sum/

Complexity:

Time: O(n)

Space: O(n)

"""

from __future__ import annotations

def two_sum(array: list[int], target: int) -> tuple[int, int] | None:

"""Find two indices whose corresponding values sum to target.

Args:

array: List of integers to search.

target: Desired sum of two elements.

Returns:

Tuple of (index1, index2) if a pair is found, or None otherwise.

Examples:

>>> two_sum([2, 7, 11, 15], 9)

(0, 1)

"""

seen = {}

for index, num in enumerate(array):

if num in seen:

return seen[num], index

else:

seen[target - num] = index

return None