Two Pointers Pattern

The Two Pointers pattern uses two indices to traverse a data structure (usually an array or linked list) in tandem. It is the most common technique for solving "In-Place" array problems with O(1) Space.

1. Opposite Direction (Meeting in the middle)

Example: "Is a string a Palindrome?" or "Reverse an array." You have a pointer at the Start and a pointer at the End. They move towards each other until they meet. This allows you to process the array in exactly N/2 steps.

2. Same Direction (Fast and Slow)

Example: "Remove duplicates from a sorted array." One pointer tracks the 'last unique element found' and the other pointer scans ahead for new values. This allows you to 'Compress' the array in a single pass without extra memory.

4. Interview Mastery

Q: "What is the advantage of Two Pointers over a simple nested loop?"

Architect Answer: "Time complexity. A nested loop for 'sum of two numbers' would be **O(N^2)**. A Two Pointer approach on a sorted array is **O(N)**. Since you only pass through the data once, it is significantly more scalable for large datasets. It also demonstrates an understanding of pointer arithmetic and memory efficiency."