feat(algorithms, dynamic programming): dynamic programming problems #151

BrianLusina · 2026-01-13T11:34:33Z

Describe your change:

Count number of palindromic substrings in a string

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

Checklist:

Summary by CodeRabbit

Documentation
- Added detailed guides for palindromic substring problems and a scheduling problem; moved Pascal's Triangle into Dynamic Programming and removed duplicate palindrome docs.
New Features
- Added palindrome-counting utilities and a minimum-machines task-scheduler.
Tests
- Added unit tests for palindrome utilities and the scheduling utility.
Style
- Minor documentation formatting cleanups.

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coderabbitai · 2026-01-13T11:34:49Z

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📥 Commits

Reviewing files that changed from the base of the PR and between 24025fa and 65dc250.

📒 Files selected for processing (4)

algorithms/dynamic_programming/palindromic_substring/README.md
algorithms/dynamic_programming/palindromic_substring/test_longest_palindromic_substring.py
algorithms/heap/schedule_tasks/README.md
algorithms/heap/schedule_tasks/test_schedule_tasks_on_minimum_machines.py

📝 Walkthrough

Walkthrough

Reorganizes palindromic substring material into a Dynamic Programming subsection, adds DP implementations and tests for counting palindromic substrings, adds a longest-palindrome test and import tweak, introduces a heap-based Schedule Tasks module with tests, and makes small docstring/README adjustments.

Changes

Cohort / File(s)	Summary
Directory & Index Updates `DIRECTORY.md`	Added Palindromic Substring and Pascal's Triangle under Dynamic Programming; removed Longest Palindromic Substring from Two Pointers; added Heap section under Spread Stones.
Palindromic Substring — docs `algorithms/dynamic_programming/palindromic_substring/README.md`	New README explaining Palindromic Substring and Longest Palindromic Substring problems and DP solution, with examples and complexity notes.
Palindromic Substring — implementations `algorithms/dynamic_programming/palindromic_substring/__init__.py`	Added `count_palindromic_substrings(s: str) -> int` and `count_palindromic_substrings_2(s: str) -> int` (DP-based, O(n²) time/space).
Longest Palindromic Substring — function `algorithms/dynamic_programming/palindromic_substring/longest_palindromic_substring.py`	Updated import to `algorithms.two_pointers.palindrome.is_palindrome`; moved former docstring text into a literal inside the function (docstring altered).
Palindromic Substring — tests `algorithms/dynamic_programming/palindromic_substring/test_palindromic_substring.py`, `algorithms/dynamic_programming/palindromic_substring/test_longest_palindromic_substring.py`	Added parameterized unit tests for counting functions and for `longest_palindromic_substring`.
Two Pointers README change `algorithms/two_pointers/palindrome/README.md`	Removed the Longest Palindromic Substring section from this README.
Pascal's Triangle — minor doc tweak `algorithms/dynamic_programming/pascals_triangle/__init__.py`	Small docstring formatting change in sequence representation.
Schedule Tasks (Heap) — docs `algorithms/heap/schedule_tasks/README.md`	New README for "Schedule Tasks on Minimum Machines" describing sorting + min-heap approach, complexities, and examples.
Schedule Tasks (Heap) — implementation `algorithms/heap/schedule_tasks/__init__.py`	Added `minimum_machines(tasks: List[List[int]]) -> int` using sorting and a min-heap to compute minimum machines (O(n log n)).
Schedule Tasks — tests `algorithms/heap/schedule_tasks/test_schedule_tasks_on_minimum_machines.py`	Added parameterized unit tests for `minimum_machines`.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

feat(algorithms, dynamic programming): dynamic programming problems #151 — Appears to make the same set of changes (palindromic_substring additions, longest_palindromic_substring import/doc tweak, Pascal's Triangle move, heap schedule_tasks and tests).
feat(algorithms, two-pointers): valid palindrome with one character removal #148 — Related changes touching palindrome code and import locations; likely connected to README/import adjustments.

Suggested labels

Heap

Poem

🐰 I hopped through code with joy and cheer,
Palindromes nested, neatly near,
Heaps stacked machines in tidy rows,
Tests awake while logic grows,
Hooray — the rabbit stamps and cheers! 🥕

🚥 Pre-merge checks | ❌ 3

❌ Failed checks (1 warning, 2 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 44.44% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Title check	❓ Inconclusive	The PR title 'feat(algorithms, dynamic programming): dynamic programming problems' is overly broad and generic. It uses vague language like 'dynamic programming problems' without clearly identifying the primary changes, which include palindromic substrings, Pascal's Triangle reorganization, and heap scheduling tasks.	Refine the title to be more specific about the main contributions, such as 'feat: add palindromic substring DP algorithms and heap scheduling tasks' or focus on the primary change if one is intended.
Description check	❓ Inconclusive	The description is partially complete but contains inaccuracies. While the author checked multiple boxes suggesting they added algorithms, fixed bugs, and made documentation changes, the description only mentions 'Count number of palindromic substrings in a string' and omits discussion of other significant changes (Pascal's Triangle reorganization, heap scheduling tasks, and removal of palindromic substring from Two Pointers).	Update the description to comprehensively document all changes: the palindromic substring algorithms, Pascal's Triangle relocation, heap scheduling implementation, and relevant documentation updates to match the extensive changes reflected in the actual commit.

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Actionable comments posted: 2

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

algorithms/dynamic_programming/palindromic_substring/longest_palindromic_substring.py (1)
32-32: Critical bug: i + i should be i + 1.

When setting the result bounds for a two-character palindrome, the end index calculation is incorrect. For phrase[i] == phrase[i + 1], the palindrome spans indices [i, i + 1], not [i, i + i].

Example: For input "aa", when i=0:

Current: result = [0, 0] → returns "a"

Expected: result = [0, 1] → returns "aa"
🐛 Proposed fix
         if phrase[i] == phrase[i + 1]:
             dp[i][i + 1] = True
-            result = [i, i + i]
+            result = [i, i + 1]

🤖 Fix all issues with AI agents

In @algorithms/dynamic_programming/palindromic_substring/README.md:
- Around line 68-69: Update the sentence that currently reads "lengths greater
than three" to "lengths greater than two" in the README explanation so it
correctly matches the algorithm description (base cases for lengths 1 and 2,
loop starts at length 3); ensure the surrounding text still reads naturally
after this single-word change.

In
@algorithms/dynamic_programming/palindromic_substring/test_longest_palindromic_substring.py:
- Around line 7-15: Add missing edge-case tests to
LONGEST_PALINDROMIC_SUBSTRING_TEST_CASES by including ("", ""), ("a", "a"), and
a length-2 palindrome case such as ("aab", "aa"); also fix the off-by-one bug in
longest_palindromic_substring.py where the center-expansion result is set with
result = [i, i + i] — change it to result = [i, i + 1] so two-character
palindromes are handled correctly (search for the variable name result and the
incorrect assignment to locate the fix).

🧹 Nitpick comments (1)

algorithms/dynamic_programming/palindromic_substring/__init__.py (1)
34-66: Consider documenting the difference between the two implementations.

Both functions produce identical results but use slightly different iteration patterns. The second function uses boolean arithmetic (count += dp[i][j]) which is a nice Pythonic touch.

It would be helpful to add a brief note in the docstring or a module-level comment explaining why two implementations exist (e.g., for educational purposes, different iteration order, etc.).
📝 Suggested docstring enhancement
 def count_palindromic_substrings_2(s: str) -> int:
     """
     Counts the number of palindromic substrings that can be found in the given string
+
+    This is an alternative implementation that iterates by substring length
+    rather than by difference between indices. Both approaches have the same
+    O(n²) time and space complexity.
+
     Args:
         s(str): string to check for palindromic substrings
     Returns:
         int: number of palindromic substrings
     """

📜 Review details

Configuration used: defaults

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 72a999a and 780f9dc.

⛔ Files ignored due to path filters (19)

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📒 Files selected for processing (10)

DIRECTORY.md
algorithms/dynamic_programming/palindromic_substring/README.md
algorithms/dynamic_programming/palindromic_substring/__init__.py
algorithms/dynamic_programming/palindromic_substring/longest_palindromic_substring.py
algorithms/dynamic_programming/palindromic_substring/test_longest_palindromic_substring.py
algorithms/dynamic_programming/palindromic_substring/test_palindromic_substring.py
algorithms/dynamic_programming/pascals_triangle/README.md
algorithms/dynamic_programming/pascals_triangle/__init__.py
algorithms/dynamic_programming/pascals_triangle/test_pascals_triangle.py
algorithms/two_pointers/palindrome/README.md

💤 Files with no reviewable changes (1)

algorithms/two_pointers/palindrome/README.md

🧰 Additional context used

🧬 Code graph analysis (1)

algorithms/dynamic_programming/palindromic_substring/test_longest_palindromic_substring.py (1)

algorithms/dynamic_programming/palindromic_substring/longest_palindromic_substring.py (1)

longest_palindromic_substring (4-42)

🪛 LanguageTool

algorithms/dynamic_programming/palindromic_substring/README.md

[style] ~23-~23: Consider a more expressive alternative.
Context: ...results of the earlier computations. To do this, we can create a lookup table, dp,...

(DO_ACHIEVE)

[style] ~43-~43: Using many exclamation marks might seem excessive (in this case: 15 exclamation marks for a text that’s 5567 characters long)
Context: ...s/palindromic_substring_solution_1.png) ![Solution 16](./images/solutions/palindr...

(EN_EXCESSIVE_EXCLAMATION)

🪛 markdownlint-cli2 (0.18.1)

algorithms/dynamic_programming/palindromic_substring/README.md

23-23: Reference links and images should use a label that is defined
Missing link or image reference definition: "j"