feat(algorithms, two-pointers): valid palindrome with one character removal

[BrianLusina]

Describe your change:

Algorithm to check if a string is a valid palindrome if at most one character is removed

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

Summary by CodeRabbit

• New Features

  • Added palindrome validation that determines if a string can become a palindrome by removing at most one character.

• Documentation

  • Added comprehensive documentation for the new palindrome validation feature with examples and complexity analysis.
  • Improved code formatting and readability in multiple algorithm documentation sections.
  • Reorganized palindrome-related algorithm references for better logical grouping.

• Tests

  • Added test cases for the new palindrome validation feature.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

The changes reorganize palindrome-related code from the Pystrings module to Two Pointers, introduce a new algorithm to validate palindromes with up to one character removal, update all import paths accordingly, and apply formatting updates to documentation files.

Changes

Cohort / File(s)	Summary
Palindrome Module Reorganization DIRECTORY.md, algorithms/two_pointers/palindrome/README.md, algorithms/two_pointers/palindrome/__init__.py, algorithms/two_pointers/palindrome/test_palindrome.py	Relocated palindrome entries from Pystrings section to Two Pointers section in directory structure. Added new is_valid_palindrome_with_one_char_removal() function with helper is_substring_palindrome() to check if a string can become a palindrome by removing at most one character. Documented algorithm with examples, complexity analysis (O(n) time, O(1) space), and solution images. Added corresponding test dataset and parameterized test class.
Import Path Updates algorithms/backtracking/partition_string/__init__.py, tests/pystrings/test_longest_palindrome.py, algorithms/two_pointers/palindrome/test_palindrome.py	Updated import sources from pystrings.palindrome to algorithms.two_pointers.palindrome across multiple files to reflect module relocation.
Documentation Formatting algorithms/greedy/jump_game/README.md, datastructures/trees/binary/README.md	Added inline code formatting (backticks) around identifiers and expressions in algorithm steps and explanations for consistency.

Poem

🐰 Palindromes hop from strings to pointers true,
With one char removal, new paths we pursue,
Imports realigned, the code finds its place,
A rabbit's refactor with elegance and grace! ✨

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly and clearly summarizes the main change: adding a new algorithm for checking valid palindromes with one character removal to the two-pointers module.
Description check	✅ Passed	The description follows the template structure with all required sections completed: change description provided, all checklist items marked as completed, and all contribution guidelines confirmed.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

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[coderabbitai]

Actionable comments posted: 2

🤖 Fix all issues with AI agents

In @algorithms/two_pointers/palindrome/README.md:
- Around line 250-252: Typo fix: update the README description for
is_valid_palindrome_with_one_char_removal to read "left_pointer at the start and
right_pointer at the end of the string" (add the missing article "the"); locate
the sentence that mentions left_pointer and right_pointer and insert "the"
before "end of the string" so the phrase becomes "at the end of the string".

In @DIRECTORY.md:
- Around line 221-232: The markdown list under the "Palindrome" section has
inconsistent indentation causing MD007 (ul-indent) errors; fix by aligning the
nesting to match the Two Pointers pattern: indent the "Palindrome" header 4
spaces, its direct children ("Largest Palindrome Product", "Longest Palindrome",
"Longest Palindromic Substring", "Palindrome Index", "Palindrome Pairs",
"Permutation Palindrome", "Test Palindrome", etc.) 6 spaces, and any test
sub-items (e.g., "Test Largest Palindrome Product", "Test Permutation
Palindrome", "Test Palindrome Index", "Test Palindrome Pairs") 8 spaces so the
list matches the surrounding sections and passes markdownlint-cli2.

🧹 Nitpick comments (2)

tests/pystrings/test_longest_palindrome.py (1)

18-24: Consider renaming test method to match the function being tested.

The method test_longest_palindrome_two (line 18) actually tests longest_palindrome_one (line 21). While this appears to be a pre-existing issue not introduced by this PR, consider renaming for clarity.

Suggested rename

-    def test_longest_palindrome_two(self):
+    def test_longest_palindrome_one_single_char(self):
         """Should return 1 for s = a"""
         s = "a"
         actual = longest_palindrome_one(s)

algorithms/two_pointers/palindrome/test_palindrome.py (1)

144-160: Good test coverage. Consider adding edge case tests.

The test cases cover a good variety of scenarios. Optionally, consider adding edge cases for completeness:

Suggested additional test cases

 IS_PALINDROME_WITH_ONE_CHAR_REMOVAL_TEST_CASES = [
+    ("a", True),      # Single character - always valid
+    ("ab", True),     # Two different chars - remove one
+    ("aa", True),     # Two same chars - already palindrome
     ("aba", True),
     ("abca", True),
     ("abc", False),
     ("abccbxa", True),
     ("madame", True),
     ("dead", True),
     ("tebbem", False),
     ("eeccccbebaeeabebccceea", False),
 ]

📜 Review details

Configuration used: defaults

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 3f016f2 and d7c2a75.

⛔ Files ignored due to path filters (9)

• algorithms/two_pointers/palindrome/images/solutions/is_valid_palindrome_with_one_char_removal_solution_1.png is excluded by !**/*.png
• algorithms/two_pointers/palindrome/images/solutions/is_valid_palindrome_with_one_char_removal_solution_2.png is excluded by !**/*.png
• algorithms/two_pointers/palindrome/images/solutions/is_valid_palindrome_with_one_char_removal_solution_3.png is excluded by !**/*.png
• algorithms/two_pointers/palindrome/images/solutions/is_valid_palindrome_with_one_char_removal_solution_4.png is excluded by !**/*.png
• algorithms/two_pointers/palindrome/images/solutions/is_valid_palindrome_with_one_char_removal_solution_5.png is excluded by !**/*.png
• algorithms/two_pointers/palindrome/images/solutions/is_valid_palindrome_with_one_char_removal_solution_6.png is excluded by !**/*.png
• algorithms/two_pointers/palindrome/images/solutions/is_valid_palindrome_with_one_char_removal_solution_7.png is excluded by !**/*.png
• algorithms/two_pointers/palindrome/images/solutions/is_valid_palindrome_with_one_char_removal_solution_8.png is excluded by !**/*.png
• algorithms/two_pointers/palindrome/images/solutions/is_valid_palindrome_with_one_char_removal_solution_9.png is excluded by !**/*.png

📒 Files selected for processing (20)

• DIRECTORY.md
• algorithms/backtracking/partition_string/__init__.py
• algorithms/greedy/jump_game/README.md
• algorithms/two_pointers/palindrome/README.md
• algorithms/two_pointers/palindrome/__init__.py
• algorithms/two_pointers/palindrome/largest_palindrome_product/README.md
• algorithms/two_pointers/palindrome/largest_palindrome_product/__init__.py
• algorithms/two_pointers/palindrome/largest_palindrome_product/test_largest_palindrome_product.py
• algorithms/two_pointers/palindrome/longest_palindrome.py
• algorithms/two_pointers/palindrome/longest_palindromic_substring.py
• algorithms/two_pointers/palindrome/palindrome_index.py
• algorithms/two_pointers/palindrome/palindrome_pairs.py
• algorithms/two_pointers/palindrome/permutation_palindrome/README.md
• algorithms/two_pointers/palindrome/permutation_palindrome/__init__.py
• algorithms/two_pointers/palindrome/permutation_palindrome/test_permutation_palindrome.py
• algorithms/two_pointers/palindrome/test_palindrome.py
• algorithms/two_pointers/palindrome/test_palindrome_index.py
• algorithms/two_pointers/palindrome/test_palindrome_pairs.py
• datastructures/trees/binary/README.md
• tests/pystrings/test_longest_palindrome.py

🧰 Additional context used

🧬 Code graph analysis (3)

algorithms/backtracking/partition_string/__init__.py (1)

algorithms/two_pointers/palindrome/__init__.py (1)

• is_palindrome (1-52)

tests/pystrings/test_longest_palindrome.py (1)

algorithms/two_pointers/palindrome/longest_palindrome.py (2)

• longest_palindrome_one (19-53)
• longest_palindrome_two (56-96)

algorithms/two_pointers/palindrome/test_palindrome.py (1)

algorithms/two_pointers/palindrome/__init__.py (1)

• is_valid_palindrome_with_one_char_removal (167-206)

🪛 markdownlint-cli2 (0.18.1)

DIRECTORY.md

221-221: Unordered list indentation
Expected: 2; Actual: 4

(MD007, ul-indent)

---

222-222: Unordered list indentation
Expected: 4; Actual: 6

(MD007, ul-indent)

---

223-223: Unordered list indentation
Expected: 6; Actual: 8

(MD007, ul-indent)

---

224-224: Unordered list indentation
Expected: 4; Actual: 6

(MD007, ul-indent)

---

225-225: Unordered list indentation
Expected: 4; Actual: 6

(MD007, ul-indent)

---

226-226: Unordered list indentation
Expected: 4; Actual: 6

(MD007, ul-indent)

---

227-227: Unordered list indentation
Expected: 4; Actual: 6

(MD007, ul-indent)

---

228-228: Unordered list indentation
Expected: 4; Actual: 6

(MD007, ul-indent)

---

229-229: Unordered list indentation
Expected: 6; Actual: 8

(MD007, ul-indent)

---

230-230: Unordered list indentation
Expected: 4; Actual: 6

(MD007, ul-indent)

---

231-231: Unordered list indentation
Expected: 4; Actual: 6

(MD007, ul-indent)

---

232-232: Unordered list indentation
Expected: 4; Actual: 6

(MD007, ul-indent)

🔇 Additional comments (8)

algorithms/greedy/jump_game/README.md (1)

70-87: Documentation formatting improvements approved.

Wrapping variable names and code expressions in backticks enhances readability and clearly distinguishes code elements from explanatory text. These formatting enhancements support better documentation clarity.

datastructures/trees/binary/README.md (1)

39-44: Documentation formatting and clarity improvements approved.

Adding inline code formatting around pointers and conditions (ptr1, ptr2, ptr1.parent, etc.) and ensuring precise punctuation placement within code notation improves the documentation's clarity and technical accuracy.

DIRECTORY.md (1)

221-232: Verify all referenced palindrome files exist in the repository.

The reorganization introduces multiple new entries and test file references under algorithms/two_pointers/palindrome/. Ensure that all paths listed are accurate and that corresponding files exist in the repository structure, particularly:

• algorithms/two_pointers/palindrome/longest_palindrome.py
• algorithms/two_pointers/palindrome/longest_palindromic_substring.py
• algorithms/two_pointers/palindrome/palindrome_index.py
• algorithms/two_pointers/palindrome/palindrome_pairs.py
• algorithms/two_pointers/palindrome/test_palindrome.py

tests/pystrings/test_longest_palindrome.py (1)

3-6: LGTM!

Import path correctly updated to reflect the new module location under algorithms.two_pointers.palindrome.

algorithms/backtracking/partition_string/__init__.py (1)

2-2: LGTM!

Import path correctly updated to reference is_palindrome from the new algorithms.two_pointers.palindrome module.

algorithms/two_pointers/palindrome/__init__.py (1)

167-206: LGTM! Well-implemented two-pointer algorithm.

The implementation correctly handles the Valid Palindrome II problem with O(n) time and O(1) space complexity. The nested is_substring_palindrome helper appropriately captures s from the enclosing scope.

One minor note: an empty string input ("") will return True since the loop condition fails immediately. This behavior seems acceptable given the problem constraints state 1 <= s.length, but consider adding an explicit check or doctest if empty string handling is important.

algorithms/two_pointers/palindrome/test_palindrome.py (1)

6-14: LGTM!

Import paths correctly updated to reference the new module location, and the new is_valid_palindrome_with_one_char_removal function is properly imported for testing.

algorithms/two_pointers/palindrome/README.md (1)

261-270: All referenced image files exist. Verification confirms that all 9 solution images are present at the specified paths in the repository.