C++ Competitive Coding Problem Solutions

I need assistance with two competitive coding questions solved in C++. The solutions should be meticulously detailed, as I require a comprehensive understanding of each step. Furthermore, the solutions must be optimized for both time and space complexity.

Ideal Skills:
- Proficient in C++
- Experience in competitive programming
- Strong problem-solving skills
- Ability to explain complex concepts in a simple manner

Please ensure that you can deliver well-explained and optimized solutions before bidding.