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analysis/04-reverse-linked-list/diagrams/README.md

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+# Reverse Linked List — PlantUML Diagrams
+
+This directory contains PlantUML diagrams for the three-pointer linked list reversal algorithm.
+
+The diagrams use a small list:
+
+```text
+1 -> 2 -> 3 -> null
+```
+
+and show how it becomes:
+
+```text
+3 -> 2 -> 1 -> null
+```
+
+## Files
+
+- `00_initial_state.puml` — initial state before the loop
+- `01_save_next.puml` — saving `next = current->next`
+- `02_reverse_current_link.puml` — reversing `current->next`
+- `03_move_pointers.puml` — moving `previous` and `current`
+- `04_second_iteration.puml` — state after the second node is processed
+- `05_final_state.puml` — final state after the loop
+
+## Generate PNG Files
+
+```sh
+plantuml diagrams/*.puml
+```
+
+## Generate SVG Files
+
+```sh
+plantuml -tsvg diagrams/*.puml
+```
+
+## Core Idea
+
+During the loop, the list is logically split into two parts:
+
+- `previous` points to the already reversed part
+- `current` points to the node currently being processed
+- `next` temporarily preserves access to the remaining original list
+
+The key operation is:
+
+```cpp
+current->next = previous;
+```
+
+But this is only safe after saving:
+
+```cpp
+Node* next = current->next;
+```
+
+Otherwise the remaining part of the original list would be lost.