02-Sliding-Window

Max Sum Subarray, Longest Substring, Smallest Subarray

Sliding Window Pattern

The Sliding Window pattern is used to perform a required operation on a specific window size of a given array or linked list, such as finding the longest subarray containing all 1s. This approach reduces the time complexity from $O(n^2)$ to $O(n)$.

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Types of Sliding Window Patterns

Scenario	How it Works	Example Problem
Fixed Size Window	Window size $K$ remains constant throughout.	Maximum Average Subarray I
Variable Size Window (Longest)	Window expands until a condition is met, then shrinks to find the max length.	Longest Substring Without Repeating Characters
Variable Size Window (Shortest)	Window expands until a condition is met, then shrinks as much as possible to find the min length.	Minimum Size Subarray Sum

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🧠 How to Identify Sliding Window Problems?

Look for these "triggers" in a question:

✅ 1. Contiguous Subarray/Substring

• "Find the longest/shortest/maximum/minimum..."
• "Continuous elements in an array or string."

✅ 2. Target Sum or Property

• "Subarray sum equals $K$."
• "At most $K$ unique characters."

✅ 3. Fixed Range Mentioned

• "Check every window of size $K$."

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🔥 Quick Mental Checklist

When you see an array or string:

• ❓ Am I looking for a continuous range (subarray/substring)?
• ❓ Does the problem ask for an optimal length (longest/shortest)?
• ❓ Can I track the "state" of the window as I slide it (sum, frequency, unique elements)?

👉 If YES, use Sliding Window.