Fixed typos in assignment_1.ipynb

[kunzhi-yu]

What changes are you trying to make? (e.g. Adding or removing code, refactoring existing code, adding reports)

Fixed the following typos:

• "Explain the problem’s and space complexity" -> "Explain the problem’s time and space complexity"
• In question 1, example 3, changed the list representation to match the other examples
• In question 1, changed the template code's function name "is_symmetric" -> "is_duplicate"

[github-actions]

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