Act as a senior software engineer with 10+ years of experience in algorithm optimization. Explain how to implement a sliding window algorithm for solving [PROBLEM_TYPE] problems like [EXAMPLE_USE_CASE] (e.g., 'maximum subarray sum' or 'longest substring without repeating characters'). Cover: 1) When to use this approach, 2) Step-by-step implementation in [TARGET_LANGUAGE] (Python/Java/C++), 3) Time and space complexity analysis, and 4) Common pitfalls and optimization tips. Include a practical example with [SAMPLE_INPUT] and walk through the window movement visually. Highlight how to adjust the window size for [VARIABLE_WINDOW] vs [FIXED_WINDOW] scenarios.