Bug fixes and improvements (#1348)

* Add "reference" for EN version. Bug fixes.

* Unify the figure reference as "the figure below" and "the figure above".
Bug fixes.

* Format the EN markdown files.

* Replace "" with <u></u> for EN version and bug fixes

* Fix biary_tree_dfs.png

* Fix biary_tree_dfs.png

* Fix zh-hant/biary_tree_dfs.png

* Fix heap_sort_step1.png

* Sync zh and zh-hant versions.

* Bug fixes

* Fix EN figures

* Bug fixes

* Fix the figure labels for EN version

en/docs/chapter_data_structure/classification_of_data_structure.md

@@ -11,14 +11,13 @@ As shown in the figure below, logical structures can be divided into two major c
 - **Linear data structures**: Arrays, Linked Lists, Stacks, Queues, Hash Tables.
 - **Non-linear data structures**: Trees, Heaps, Graphs, Hash Tables.
 
-![Linear and non-linear data structures](classification_of_data_structure.assets/classification_logic_structure.png)
-
 Non-linear data structures can be further divided into tree structures and network structures.
 
-- **Linear structures**: Arrays, linked lists, queues, stacks, and hash tables, where elements have a one-to-one sequential relationship.
 - **Tree structures**: Trees, Heaps, Hash Tables, where elements have a one-to-many relationship.
 - **Network structures**: Graphs, where elements have a many-to-many relationships.
 
+![Linear and non-linear data structures](classification_of_data_structure.assets/classification_logic_structure.png)
+
 ## Physical structure: contiguous and dispersed
 
 **During the execution of an algorithm, the data being processed is stored in memory**. The figure below shows a computer memory stick where each black square is a physical memory space. We can think of memory as a vast Excel spreadsheet, with each cell capable of storing a certain amount of data.
@@ -38,6 +37,7 @@ As illustrated in the figure below, **the physical structure reflects the way da
 ![Contiguous space storage and dispersed space storage](classification_of_data_structure.assets/classification_phisical_structure.png)
 
 **It is worth noting that all data structures are implemented based on arrays, linked lists, or a combination of both**. For example, stacks and queues can be implemented using either arrays or linked lists; while implementations of hash tables may involve both arrays and linked lists.
+
 - **Array-based implementations**: Stacks, Queues, Hash Tables, Trees, Heaps, Graphs, Matrices, Tensors (arrays with dimensions $\geq 3$).
 - **Linked-list-based implementations**: Stacks, Queues, Hash Tables, Trees, Heaps, Graphs, etc.