Update: Classification Issue of Hash Tables

[huoyinghui]

Pull Request Description

This pull request (PR) addresses a potential misclassification issue in the documentation under the section Classification of Data Structures. Specifically, the classification of hash tables as a non-linear data structure has been corrected to avoid confusion.

Summary of Changes
1. Corrected Classification:
• Removed hash tables from the “non-linear data structure” category.
• Explicitly listed hash tables only under the “linear data structure” category.
2. Clarified Tree Structure:
• Updated the definition of “tree structure” to remove hash tables as an example, as their logical structure does not fit the hierarchical one-to-many relationship of trees.
3. Updated Visual Consistency:
• Ensured the accompanying text aligns with the corrected classification.

Purpose of the Change

The prior classification incorrectly suggested that hash tables belong to non-linear data structures, which could confuse readers. This update aligns with the widely accepted understanding that hash tables are logically linear, even though their implementation may sometimes use non-linear techniques (e.g., chaining with linked lists).

Checklist
• I have thoroughly reviewed the updated content for accuracy and clarity.
• The updated content aligns with widely accepted conventions for data structure classifications.
• The changes ensure that future readers will have a more precise understanding of hash tables and their classification.