Implement Factorial and Squares

Write two Python functions for a live coding interview: 1. `factorial(n)`: Given a non-negative integer `n`, return `n!`. Implement it iteratively, and be prepared to explain how a recursive version would differ. State the time and space complexity. 2. `squares(n)`: Given a non-negative integer `n`, return a list of squares of the first `n` integers. Clearly state your convention—either `[0^2, 1^2, ..., (n-1)^2]` or `[1^2, 2^2, ..., n^2]`—and handle edge cases such as `n = 0` or invalid negative input.