Add tests and refactor code smells for algorithms

[nientbfx07802]

Summary

This PR adds comprehensive unit tests and refactors code smells across multiple algorithm implementations.

Changes

• New Tests: Added test suites for BuySellStocks, ClosestBinarySearchTreeValue, RansomNote, and ShortestWordDistanceIII
• Refactoring: Improved code quality in ShortestWordDistanceIII by extracting a boolean flag to reduce complexity and enhance readability

Details

Tests Added:

• BuySellStocks: 5 test cases covering edge cases and profit calculations
• ClosestBinarySearchTreeValue: 6 test cases for tree traversal and value proximity
• RansomNote: 6 test cases for character availability validation
• ShortestWordDistanceIII: 6 test cases for word distance calculations

Code Refactoring:

• Simplified ShortestWordDistanceIII logic by introducing isSameWord boolean to reduce nested conditions
• Improved code readability with clearer comments