Two pointers and sliding window in Java — the pattern that shows up everywhere...

Short summary

This tutorial explains two-pointer and sliding-window algorithmic patterns in Java with concrete code examples. Two pointers use two index variables moving toward each other or in the same direction to reduce O(n²) problems to O(n), while sliding window optimizes contiguous subarray/substring problems by incrementally adjusting a window instead of recomputing from scratch. A decision table helps readers pick the right technique based on problem characteristics like sorted arrays, in-place modification, or fixed-length subarrays.

• •Two pointers reduce O(n²) pair-finding to O(n) using opposite-end or same-direction traversal
• •Sliding window optimizes contiguous subarray/substring problems by incremental adjustment
• •Decision table maps problem types to the appropriate technique

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