Improve minimum-deletions-to-make-string-balanced space complexity to O(1)

[yamcodes]

Closes #18

Summary by CodeRabbit

• Documentation
  • Expanded docs and README to describe multiple solution variants, progression notes, and updated metadata.
• New Features
  • Added several alternative solution variants (naive, DP scaffold, memoized, prefix/suffix, recursive) as distinct approaches.
• Performance
  • Optimized the primary solution to a single-pass constant-space implementation.
• Tests
  • Introduced shared test data and dedicated parameterized test classes for each solution; some scaffolded tests are currently disabled.

[coderabbitai]

Caution

Review failed

The pull request is closed.

Walkthrough

Refactors the primary solution to a single-pass O(1) space implementation, adds multiple solution variants (naive, prefix/suffix, recursive, memoized, DP scaffold), centralizes test data in TestCases.java, introduces per-variant parameterized tests (many disabled/placeholders), and updates documentation and IDE run configuration.

Changes

Cohort / File(s)	Summary
Core Solution src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/Solution.java	Replaced previous split-based approach with a single-pass O(1) space implementation; removed getSliceInfo and minimumDeletionsNaive.
Additional Solution Variants src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionNaive.java, .../SolutionPrefixSuffix.java, .../SolutionRecursive.java, .../SolutionMemoized.java, .../SolutionDp.java	Added multiple variant implementations: naive (O(n²)), prefix/suffix (O(n) time, O(n) space), recursive/memoized stubs (unimplemented), and a DP scaffold (throws UnsupportedOperationException).
Tests: centralization & per-variant src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/TestCases.java, SolutionTest.java, SolutionNaiveTest.java, SolutionPrefixSuffixTest.java, SolutionRecursiveTest.java, SolutionMemoizedTest.java, SolutionDpTest.java	Introduced TestCases provider used via @MethodSource and added parameterized test classes for each solution variant; several tests are annotated @Disabled and some reference unimplemented variants. SolutionTest made package-private and simplified to use centralized cases.
Docs & Metadata README.md, CLAUDE.md, src/main/java/.../package-info.java	Expanded documentation to describe multi-solution layout, prefix-based naming, progression notes, and updated complexity claims (Solution now O(1) space).
IDE Config .idea/runConfigurations/Test_All.xml	Renamed JUnit run configuration from "Test" to "Test All".

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• Implement minimum-deletions-to-make-string-balanced #8 — touched the per-split naive implementation (getSliceInfo / O(n²) that was extracted into SolutionNaive`.
• Refactor minimum deletions to use O(n) time #10 — modifies the core minimumDeletions implementation similarly; related edits to Solution.java.
• Improve minimum-deletions-to-make-string-balanced space complexity to O(1) #20 — replaces O(n) prefix/suffix implementation with a single-pass O(1) version and adds solution variants/tests.

Poem

🐰 Hopping through code with a carrot of glee,
I trimmed needless arrays to keep things O(1) — whee!
Naive, DP, and prefixes lined up in a row,
Tests gathered together so each method can show.
Tiny paws, big refactor — onward I go! 🥕

🚥 Pre-merge checks | ✅ 4 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The PR includes extensive out-of-scope changes: documentation updates (CLAUDE.md, README.md, package-info.java), IDE config changes (.idea/runConfigurations/Test_All.xml), test infrastructure (TestCases.java shared data), and multiple alternative solution scaffolds (SolutionNaive, SolutionDp, SolutionMemoized, SolutionRecursive, SolutionPrefixSuffix) not mentioned in issue #18.	Consider separating the O(1) space optimization for Solution.java from documentation updates and alternative solution scaffolds into focused pull requests with specific issues.
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 (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main objective: improving space complexity from O(n) to O(1) for the minimum-deletions solution, which is clearly reflected in the Solution.java changes.
Linked Issues check	✅ Passed	The PR successfully implements the primary requirement from issue #18: the Solution.java file now uses an O(1) space, single-pass DP approach tracking counters instead of prefix/suffix arrays.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into main

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch 18-improve-minimum-deletions-space-complexity-to-o1

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[coderabbitai]

Actionable comments posted: 1

Caution

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

⚠️ Outside diff range comments (1)

README.md (1)

13-13: ⚠️ Potential issue | 🟡 Minor

Update README.md to reflect O(1) space complexity for problem 1653.

The Solution.java now correctly uses O(1) space (as shown in its Javadoc), but the solutions table still shows the stale O(n) value. Update line 13 in README.md to match.

Proposed fix

-| 1653 | [Minimum Deletions to Make String Balanced](https://leetcode.com/problems/minimum-deletions-to-make-string-balanced/) | Medium     | `O(n)`            | `O(n)` |
+| 1653 | [Minimum Deletions to Make String Balanced](https://leetcode.com/problems/minimum-deletions-to-make-string-balanced/) | Medium     | `O(n)`            | `O(1)` |

🤖 Fix all issues with AI agents

In
`@src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/Solution.java`:
- Line 6: Update the Javadoc in Solution.java to stop claiming it "Optimizes
{`@code` SolutionDp}" since SolutionDp is unimplemented; edit the summary to
accurately describe the implemented algorithm (e.g., "Uses a
split-point/counting approach to compute minimum deletions in constant space")
or remove the DP reference, and ensure the Javadoc mentions the current approach
by name so readers are not misled by the unimplemented class {`@code` SolutionDp}
or the TODO in package-info.java.

🧹 Nitpick comments (4)

src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/package-info.java (1)

26-31: Documentation contradicts itself about Solution's approach.

Line 26 lists Solution as "Space-optimized DP, O(n) time, O(1) space" in the DP progression, but lines 29–31 state it currently uses a split-point approach and should later be replaced with the DP formulation. This is confusing for readers — Solution appears in the DP progression list despite not being DP yet.

Consider either removing Solution from the DP progression until it actually uses DP, or clarifying the current listing (e.g., placeholder entry marked as "planned").

src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/TestCases.java (1)

11-19: Consider adding edge cases for empty string and already-balanced inputs.

The test suite covers a good variety of patterns but misses a few boundary cases: "" (empty → 0), "a" (single char → 0), and "ab" (already balanced → 0). These help catch off-by-one or empty-input issues.

CLAUDE.md (1)

28-34: Add a language specifier to the fenced code block.

Static analysis (markdownlint MD040) flags this code block as missing a language identifier. Adding text or leaving it consistent with the other directory-tree block above would resolve the warning.

Proposed fix

-```
+```text
 src/test/java/codes/yam/leetcode/{problemslug}/
 ├── TestCases.java          # Shared test data (static Stream<Arguments> cases())
 ├── SolutionTest.java       # Tests Solution.java
 ├── SolutionNaiveTest.java  # Tests SolutionNaive.java (one test file per solution)
 └── SolutionDpTest.java
-```
+```

src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/Solution.java (1)

20-35: The algorithm is correct but non-obvious — consider adding a brief explanatory comment.

The split-point tracking logic with aAfter, bBefore, and the reset condition is clever but not immediately intuitive. A short comment explaining the invariant (e.g., "track the cost of the best split point seen so far; reset when deleting all b's becomes cheaper") would help future readers.