feat: add Longest Palindromic Substring (#23)

Author: wislertt

.amazonq/rules/problem-creation.md

@@ -32,13 +32,19 @@ poetry run python .templates/leetcode/scrape.py -s "two-sum"
 
 Required fields for `.templates/leetcode/json/{problem_name}.json`:
 
+**CRITICAL: Use single quotes for Python strings in playground fields to avoid JSON escaping issues with Jupyter notebooks.**
+
+**JSON Escaping Rules:**
+
+- `playground_test_case`: Use single quotes for string literals (e.g., `s = 'hello'` not `s = "hello"`)
+- `playground_execution`: Use single quotes for string literals
+- `playground_assertion`: Use single quotes for string literals
+- Double quotes in JSON + cookiecutter + Jupyter notebook = triple escaping issues
+
 **Reference examples in `.templates/leetcode/examples/` for complete templates:**
 
-- `basic.json5` - Array, string, number problems
+- `basic.json5` - All standard problems (array, string, tree, linked list, etc.)
 - `design.json5` - Data structure design problems (LRU Cache, etc.)
-- `tree.json5` - Binary tree problems
-- `linked_list.json5` - Linked list problems
-- `matrix.json5` - 2D array/matrix problems
 
 ````json
 {

.templates/leetcode/examples/README.md

@@ -1,117 +1,41 @@
-# LeetCode Problem Template Examples
+# JSON Template Examples
 
-This directory contains comprehensive JSON5 template examples for different types of LeetCode problems. These examples serve as references when creating new problems using the universal cookiecutter template.
+This directory contains comprehensive examples for creating LeetCode problem templates.
 
-## Template Types
+## Files
 
-### 1. `basic.json5` - Basic Algorithm Problems
+- **`basic.json5`** - Covers all standard problem types:
+    - Array problems (Container With Most Water)
+    - String problems (with JSON escaping notes)
+    - Tree problems (import and parameter examples)
+    - Linked list problems (import and parameter examples)
+    - Matrix problems
+    - Number problems
 
-**Use for:** Array, string, number, hash table problems
-**Examples:** Container With Most Water, Two Sum, Valid Palindrome
-**Key features:**
+- **`design.json5`** - Data structure design problems:
+    - Custom class names (LRUCache, not Solution)
+    - Multiple methods including `__init__`
+    - Complex test setup with operation sequences
+    - Custom imports
 
-- Simple `Solution` class with single method
-- Standard test parametrization
-- Basic playground setup
+## Key Differences
 
-### 2. `tree.json5` - Binary Tree Problems
+### Standard Problems (basic.json5)
 
-**Use for:** Binary tree, BST, tree traversal problems
-**Examples:** Invert Binary Tree, Maximum Depth, Serialize Tree
-**Key features:**
+- `solution_class_name`: Always "Solution"
+- Single method (usually)
+- Simple test cases with direct assertions
+- Standard imports
 
-- `TreeNode` imports and conversions
-- `TreeNode.from_list()` and `TreeNode.to_list()` in tests
-- Tree visualization support
+### Design Problems (design.json5)
 
-### 3. `linked_list.json5` - Linked List Problems
+- `solution_class_name`: Custom class name (e.g., "LRUCache")
+- Multiple methods including constructor
+- Operation sequence testing
+- Import custom class in tests
 
-**Use for:** Singly/doubly linked list problems
-**Examples:** Reverse Linked List, Merge Lists, Detect Cycle
-**Key features:**
+## Critical Notes
 
-- `ListNode` imports and conversions
-- `ListNode.from_list()` and `ListNode.to_list()` in tests
-- Arrow visualization support
-
-### 4. `design.json5` - Data Structure Design Problems
-
-**Use for:** Design problems requiring custom classes
-**Examples:** LRU Cache, Implement Trie, Design HashMap
-**Key features:**
-
-- Custom class names (not `Solution`)
-- Multiple methods including `__init__`
-- Complex operation sequence testing
-- Type annotations for complex test logic
-
-### 5. `matrix.json5` - 2D Array/Matrix Problems
-
-**Use for:** Matrix manipulation, 2D array problems
-**Examples:** Spiral Matrix, Rotate Image, Search 2D Matrix
-**Key features:**
-
-- 2D array type annotations (`list[list[int]]`)
-- Visual examples with images
-- Matrix-specific test cases
-
-## Usage Guidelines
-
-### Problem Type Detection
-
-1. **Basic**: Single algorithm, simple input/output
-2. **Tree**: Mentions "tree", "node", uses tree terminology
-3. **Linked List**: Mentions "linked list", "node", list operations
-4. **Design**: "Design", "Implement", multiple operations
-5. **Matrix**: "matrix", "2D array", "grid", visual layout
-
-### Key Template Fields
-
-#### Required Fields
-
-- `problem_name`: snake_case identifier
-- `solution_class_name`: "Solution" or custom class name
-- `problem_number`: LeetCode number as string
-- `problem_title`: Exact LeetCode title
-- `difficulty`: "Easy", "Medium", or "Hard"
-- `topics`: Comma-separated topic string
-- `solution_methods`: Array of method definitions
-
-#### Important Patterns
-
-- **Type Hints**: Use modern syntax (`list[int]`, `dict[str, int]`, `Type | None`)
-- **Method Names**: Always snake_case
-- **Test Cases**: String representation of Python data structures
-- **Imports**: Include necessary helper classes (TreeNode, ListNode)
-
-#### PascalCase Naming Rules
-
-For `solution_class_name` and `test_class_name` properties:
-
-- **Acronyms**: Keep all caps ("LRUCache" not "LruCache")
-- **Roman numerals**: Keep all caps ("ReverseLinkedListII" not "ReverseLinkedListIi")
-- **Common patterns**: "BST", "DFS", "BFS", "API", "URL", "HTML", "JSON", "XML"
-
-### Template Selection Process
-
-1. Identify problem type from description/title
-2. Choose appropriate template from examples
-3. Customize fields for specific problem
-4. Ensure imports match problem requirements
-5. Verify test setup matches data structures used
-
-## Validation
-
-All templates are validated against:
-
-- Cookiecutter template compatibility
-- Linting requirements (black, isort, ruff, mypy)
-- Test framework integration
-- Notebook JSON format compliance
-
-## Notes
-
-- JSON5 format allows comments for documentation
-- All examples are based on working, tested templates
-- Templates are designed for the universal cookiecutter system
-- Examples include both simple and complex problem patterns
+- **JSON Escaping**: Use single quotes for Python strings in playground fields
+- **Type Hints**: Use modern syntax (`list[int]`, `TreeNode | None`)
+- **PascalCase**: Keep acronyms ALL CAPS (LRUCache, ReverseLinkedListII)

.templates/leetcode/examples/basic.json5

@@ -37,13 +37,22 @@
   "readme_additional": "",                           // Optional: additional notes, follow-up questions
 
   // === SOLUTION TEMPLATE ===
-  "solution_imports": "",                            // Empty for basic problems, add imports if needed
+  "solution_imports": "",                            // Empty for basic problems
+                                                    // For tree: "from leetcode_py import TreeNode"
+                                                    // For linked list: "from leetcode_py import ListNode"
   "solution_methods": [
     {
       "name": "max_area",                           // snake_case method name
       "parameters": "height: list[int]",            // Modern Python type hints (list[int], not List[int])
+                                                    // For tree: "root: TreeNode | None"
+                                                    // For linked list: "head: ListNode | None"
+                                                    // For string: "s: str"
       "return_type": "int",                         // Return type annotation
-      "dummy_return": "0"                           // Default return value (auto-set by generator)
+      "dummy_return": "0"                           // Default return value
+                                                    // For string: "\"\""
+                                                    // For bool: "False"
+                                                    // For list: "[]"
+                                                    // For tree/linked list: "None"
     }
   ],
 
@@ -68,8 +77,12 @@
   ],
 
   // === PLAYGROUND NOTEBOOK ===
+  // CRITICAL: Use single quotes for Python strings to avoid JSON escaping issues with Jupyter notebooks
+  // Double quotes in JSON + cookiecutter + Jupyter notebook = triple escaping issues
   "playground_imports": "from solution import Solution",
   "playground_test_case": "# Example test case\nheight = [1,8,6,2,5,4,8,3,7]\nexpected = 49",
+                                                    // For string problems: "s = 'hello'\nexpected = 'olleh'"
+                                                    // For tree: "root_list = [3,9,20,None,None,15,7]\nroot = TreeNode.from_list(root_list)"
   "playground_execution": "result = Solution().max_area(height)\nresult",
   "playground_assertion": "assert result == expected"
 }

.templates/leetcode/examples/design.json5

@@ -75,7 +75,8 @@
     ],
 
     // === PLAYGROUND NOTEBOOK ===
-    // IMPORTANT: Design playground uses operation sequences like tests
+    // CRITICAL: Use single quotes for Python strings to avoid JSON escaping issues with Jupyter notebooks
+    // Double quotes in JSON + cookiecutter + Jupyter notebook = triple escaping issues
     playground_imports: "from solution import LRUCache",
     playground_test_case: "# Example test case\noperations = ['LRUCache', 'put', 'put', 'get', 'put', 'get', 'put', 'get', 'get', 'get']\ninputs = [[2], [1, 1], [2, 2], [1], [3, 3], [2], [4, 4], [1], [3], [4]]\nexpected = [None, None, None, 1, None, -1, None, -1, 3, 4]",
     playground_execution: "cache = None\nresults: list[int | None] = []\nfor i, op in enumerate(operations):\n    if op == 'LRUCache':\n        cache = LRUCache(inputs[i][0])\n        results.append(None)\n    elif op == 'get' and cache is not None:\n        results.append(cache.get(inputs[i][0]))\n    elif op == 'put' and cache is not None:\n        cache.put(inputs[i][0], inputs[i][1])\n        results.append(None)\nresults",