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Technical Interview Problems in Python: Lists
Pair Sum: Naive

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 + nums == 8
# [1, 4]

pair_sum(nums, 17)
# nums + nums == 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!

### Instructions

1.

Write a function `pair_sum()`, which has two parameters: `nums` and `target`.

`pair_sum()` should return a list containing a pair of indices whose values sum to `target`.

If no such pair of indices exists, return `None`.