feat: add beginner-friendly solutions and educational flashcards

[Z41N-B1N-KH4L1D]

Overview

This pull request introduces missing solutions and refines existing ones to better support beginners. It also includes a new set of flashcards designed to reinforce core concepts.

Key Changes

• New Solutions: Added implementations for previously missing exercises.
• Beginner Optimizations: Refactored complex code into more readable, entry-level versions for clearer understanding.
• Learning Tools: Integrated a set of flashcards for active recall.

Additional Notes

• Future Updates: I plan to expand the flashcard library and add more solutions following a short break to finalize other development projects.
• Context: As a long-term learner of this community, I wanted to contribute back by making the repository more accessible to those just starting their journey.