We’ll end with a classic interview question: given a list of integers and a “target” integer, return a pair of indices whose values sum to the target.

nums = [4, 2, 8, 9, 6]
target = 8

pair_sum(nums, target)
# nums[1] + nums[4] == 8
# [1, 4]

pair_sum(nums, 17)
# nums[2] + nums[3] == 17
# [2, 3]

pair_sum(nums, 99)
# no pair sum exists...
# None

Clarifying Questions:

• Are there constraints on time or space efficiency?
  • No! Any solution will do.
• Can the numbers be negative or 0?
  • Yes! Your solution should handle those inputs.
• Does the order of indices matter?
  • The earlier index comes first in the return list.
• Do we return all pairs that match a solution?
  • No! The first one that your solution finds will do!