Validate FastSort stdin bounds

[krotname]

Motivation

• Prevent an availability issue where untrusted stdin could drive unchecked allocations or unbounded token accumulation causing OutOfMemoryError or NegativeArraySizeException in the FastSort CLI.
• Ensure parsing of numeric and string tokens from stdin is validated and bounded before any heap allocation is performed.

Description

• Add MAX_PARTICIPANTS and MAX_LOGIN_LENGTH constants and apply them in the CLI run path to limit allocations and token sizes.
• Replace the unsafe nextInt() with nextInt(String fieldName, int minValue, int maxValue) that enforces digit-only input, overflow checks, and min/max bounds.
• Replace the unbounded next() with next(int maxLength) and introduce nextNonWhitespace() so tokens are read with a maximum length check and fail early if exceeded.
• Wire the new bounded parsers into run() so the Participant[] allocation and each login/solved/penalty read are validated while preserving existing sorting behavior for valid inputs.

Testing

• Ran mvn test which completed successfully (BUILD SUCCESS, 546 tests run) and all unit tests passed.
• Compiled the changed file with javac -g src/main/java/algorithms/sprint3/FastSort.java which succeeded.
• Performed manual CLI checks: a normal sample input produced expected output, and malformed/oversized inputs such as 2147483648, 1000000000 and an excessively long login token produced validation IOException and non-zero exit as expected.

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Codex Task

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[krotname]

Superseded by the validated combined merge in #115: #115