Harden Solution2 stdin handling

[krotname]

Motivation

• Prevent uncaught NullPointerException when the declared stdin line count does not match supplied input.
• Avoid unbounded memory allocation from accumulating all outputs in a single StringBuilder, which can lead to OOM for attacker-controlled large input.
• Enforce token and numeric validation to avoid malformed input being silently processed or causing unexpected behavior.

Description

• Added MAX_LINE_COUNT limit and readLineCount, readInputLine, and nextToken helpers to validate the declared line count, EOF, and token availability in src/main/java/algorithms/sprint1/Solution2.java.
• Replaced output accumulation with streaming to stdout using a PrintWriter to eliminate unbounded StringBuilder growth and preserved the expected trailing blank line.
• Validated token counts and numeric parsing, replaced addition with Math.addExact for safer arithmetic, and throw IllegalArgumentException on malformed input.
• Added regression tests in src/test/java/algorithms/AlgorithmCliTest.java to assert that missing input lines and oversized line counts are rejected.

Testing

• Ran mvn -q -Dtest=AlgorithmCliTest test, which passed after the fix.
• Ran mvn -q test, which completed successfully.
• Ran mvn -q verify, which completed successfully and includes the new integration checks for Solution2.

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Codex Task

[codecov]

Codecov Report

❌ Patch coverage is 73.07692% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/main/java/algorithms/sprint1/Solution2.java	73.07%	3 Missing and 4 partials ⚠️

📢 Thoughts on this report? Let us know!

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
81.6% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[krotname]

Superseded by the validated combined merge in #115: #115