Yes, solving previous years question papers of UPSC Mathematics optional subject can significantly improve your problem-solving efficiency. Here's how:

1. Familiarity with Exam Pattern:
- Solving previous years' papers helps you become familiar with the exam pattern, the types of questions asked, and the distribution of marks.
- You get an idea of the weightage given to different topics, allowing you to prioritize your preparation accordingly.

2. Understanding the Question Style:
- UPSC question papers often have a unique style and format. By solving previous papers, you become familiar with this style and learn how to approach different types of questions effectively.
- You become better at interpreting complex questions, identifying the key concepts, and formulating a logical solution strategy.

3. Identifying Important Topics:
- Previous years' papers can help you identify the topics that are frequently asked in the exam.
- By analyzing the question papers, you can prioritize your preparation and focus more on the important topics, ensuring that you have a strong foundation in those areas.

4. Enhancing Speed and Accuracy:
- Solving previous years' papers regularly helps in improving your speed and accuracy in solving mathematical problems.
- You become more efficient in applying the concepts, formulas, and techniques to solve problems within the given time constraints.

5. Testing Self-Assessment:
- Solving previous years' papers allows you to assess your own performance and identify areas where you need improvement.
- You can evaluate your strengths and weaknesses, and accordingly modify your study plan to focus on the areas that require more attention.

6. Gaining Confidence:
- By solving previous years' papers, you become more confident in your problem-solving abilities.
- You develop a better understanding of the subject, which boosts your confidence during the actual exam.

7. Time Management Skills:
- Solving previous years' papers helps in developing effective time management skills.
- You learn how to allocate time to different sections of the question paper, ensuring that you complete the exam within the given time frame.

In conclusion, solving previous years' question papers of UPSC Mathematics optional subject is an excellent strategy to enhance your problem-solving efficiency. It helps you understand the exam pattern, familiarize yourself with the question style, identify important topics, improve speed and accuracy, assess your performance, gain confidence, and develop time management skills. Regular practice of previous years' papers will undoubtedly contribute to your success in the UPSC Mathematics optional subject exam.