Day 25 — Two Pointers

What you’ll learn here

• The two flavors: same direction (sliding window) and opposite ends (converging)
• Classic problems: pair sum in a sorted array, Dutch national flag, container with most water, three-sum
• When you need to sort first to enable the technique
• Handling duplicates without producing duplicate answers

Two-pointer techniques routinely turn O(n²) brute force into O(n) — and they cost nothing beyond two integer variables.