Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the mutation and copying bugs pattern
Assignment does not copy, a shallow copy still shares its contents, and mutating methods return None.
What went wrong: [row] * rows puts the same row in the grid several times. Changing one changes them all.
The fix: seats = [[0] * cols for _ in range(rows)]
Remember: never use * to repeat a list of lists. Use a list comprehension.
The pattern behind it: mutation and copying bugs.
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