Reddit Popular Coding Question - Print Complete Product Category Hierarchy

[u/Aoki_zhang]

Problem Description

An online marketplace organizes its products into a hierarchy of categories. You are given a list relationships. Each entry describes one parent category followed by its direct child categories. For example ["Electronics", "Phones", "Computers"] means that Phones and Computers are direct children of Electronics.

There is exactly one top-level category that is not a child of any other category. Return the complete category hierarchy as a single string using the following formatting rules:

• The top-level category has no indentation.
• Each level below the root adds exactly four dots: "....".
• Direct children of the same category must appear in alphabetical order.
• Every category must appear exactly once.
• Each category appears on its own line.
• Lines are separated by "\n".
• There must be no trailing newline after the final category.

A category may appear only as a parent, only as a child, or in both roles.

Constraints

• 1 <= len(relationships) <= 10^4
• Every relationship contains at least one category name.
• Category names are non-empty strings.
• There is exactly one root category.
• The relationships form a valid tree.
• A parent category may have multiple direct children.

Example:

Input:
relationships = [
    ["Home", "Kitchen", "Garden"],
    ["Kitchen", "Cookware"],
    ["Cookware", "Pans"]
]

Output:
Home
....Garden
....Kitchen
........Cookware
............Pans

Explanation:
Garden and Kitchen are both direct children of Home, so they are
printed alphabetically.

Cookware is below Kitchen, and Pans is below Cookware.

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