Add sliding-window module: 12 sliding window and two-pointer interview problems, brute-force cross-checks, dry-run traces, operation counts, pitfalls (11 tests)

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b6EqSkUWKNBc8i3Q3U

sliding-window/README.md

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+# sliding-window
+
+Companion code for the ankurm.com article **Sliding Window and Two Pointers in Java: 12 Interview Problems Solved**.
+
+Twelve classic interview problems solved with the two patterns, each cross-checked against an
+obviously-correct brute-force version on seeded random inputs. Every figure and console line in
+the article is quoted from a file in `output/`, which the JUnit tests write while asserting the
+same numbers. There is no `docs/` folder: the explanations live in the article itself.
+
+## Versions
+
+| Component | Version | Verified against |
+|---|---|---|
+| JDK | Temurin 25.0.5+8 (LTS) | `java -version` |
+| JUnit | 6.1.3 | `junit-bom` `maven-metadata.xml` on Maven Central (latest GA) |
+| Maven | 3.9.x | `mvn -version` |
+
+## Quickstart
+
+```bash
+cd sliding-window
+export JAVA_HOME=/path/to/jdk-25 PATH="$JAVA_HOME/bin:$PATH"
+./scripts/run-all.sh      # runs 11 tests and regenerates output/*.txt
+```
+
+The first Maven run must be online so the plugins land in the local cache.
+
+## The twelve problems
+
+| # | Problem | Pattern | Method |
+|---|---|---|---|
+| 1 | Maximum sum of k consecutive elements | fixed window | `FixedWindow.maxSumSubarray` |
+| 2 | Permutation in string | fixed window + counts | `FixedWindow.permutationInString` |
+| 3 | Sliding window maximum | fixed window + monotonic deque | `FixedWindow.slidingWindowMaximum` |
+| 4 | Longest substring without repeating characters | variable window | `VariableWindow.longestUniqueSubstring` |
+| 5 | Longest substring with at most K distinct characters | variable window | `VariableWindow.longestKDistinct` |
+| 6 | Longest repeating character replacement | variable window | `VariableWindow.characterReplacement` |
+| 7 | Max consecutive ones III | variable window | `VariableWindow.longestOnes` |
+| 8 | Minimum size subarray sum | shrinking window | `VariableWindow.minSubArrayLen` |
+| 9 | Minimum window substring | shrinking window | `VariableWindow.minWindow` |
+| 10 | Two Sum II (sorted input) | opposite-end pointers | `TwoPointers.twoSumSorted` |
+| 11 | 3Sum | sort + pointers | `TwoPointers.threeSum` |
+| 12 | Container with most water | opposite-end pointers | `TwoPointers.maxArea` |
+
+## Source layout
+
+```
+sliding-window/
+├── pom.xml
+├── scripts/run-all.sh
+├── src/main/java/com/ankurm/interviewlab/slidingwindow/
+│   ├── FixedWindow.java       problems 1-3
+│   ├── VariableWindow.java    problems 4-9
+│   ├── TwoPointers.java       problems 10-12
+│   ├── BruteForce.java        slow, obviously-correct references
+│   ├── DryRuns.java           instrumented copies that record every step
+│   ├── Complexity.java        operation counters (counted, not timed)
+│   └── Pitfalls.java          four plausible-looking wrong versions
+├── src/test/java/.../         SolutionsTest, RandomAgreementTest, DryRunTest, ComplexityTest, PitfallsTest
+└── output/*.txt               captured real output
+```
+
+## Captured output (`output/`)
+
+| File | What it shows |
+|---|---|
+| `01-fixed-window-trace.txt` | max-sum window sliding over `[2,1,5,1,3,2]` |
+| `02-longest-unique-trace.txt` | left pointer jumps on `abcabcbb` and the `abba` case |
+| `03-min-window-trace.txt` | grow until valid, shrink until invalid on `ADOBECODEBANC` |
+| `04-sliding-max-deque-trace.txt` | the monotonic deque contents at every step |
+| `05-two-pointers-trace.txt` | Two Sum II and Container With Most Water |
+| `06-all-twelve-results.txt` | one example per problem beside the brute-force answer |
+| `07-random-agreement.txt` | 24,000 seeded comparisons, 0 disagreements |
+| `08-operation-counts.txt` | brute force vs window operation counts at n = 1k..8k |
+| `09-pitfalls.txt` | four classic mistakes, each reproduced |