Fix problem 61 checker to expect single-integer answer (fixes #186)

[siddharthachatterjee]

Summary

Fixes issue #186.

Previous algorithmic/problems/61/check.cpp first parsed participant output d as number of segments followed by d (l, r) pairs, while statement and answer files expect a single integer output instead of listing of segments.

Fixes by reading single long long participant_score per test_case, checking if this matches ref_score. Additionally, simplified formulas for ratio and unbounded_ratio as participant_score and ref_score are guaranteed to match at that point in execution.

Type of Change

• New research problem
• New algorithmic problem
• New Frontier-CS 2.0 problem
• Bug fix
• Documentation update
• Other:

Testing

• First compiled check.cpp against judge/include/testlib.h
• Checked that original checker rejected correct sample output of 3 6 with error provided in issue description
• Confirmed that the new checker still rejects both under- and over-claim
• Ran the fixed checker against all 57 archived testdata/*.in files, feeding .ans back as the "participant" output resulting in all 57 pass.

Checklist

• Code follows the project structure and conventions
• Self-review completed
• [N/A] Documentation updated (if applicable)

CI Validation (for new problems)

N/A, only edited check.cpp

When adding new problems, CI will automatically validate that your reference solution achieves score > 0.

• Algorithmic problems: Include reference.cpp in your problem directory
• Research problems: Include reference.py (or reference.cpp if language: cpp in config.yaml)
• 2.0 problems: Include reference.py unless the problem config declares another language