Explain the two-pointer technique and its applications.

Two-pointer technique uses two indices to traverse data structure, typically moving toward each other or in same direction. Applications: Finding pair with target sum in sorted array (pointers at both ends, move based on current sum), Removing duplicates in-place (slow and fast pointers), Palindrome check, Merging sorted arrays, Sliding window problems. Reduces O(n^2) brute force to O(n) in many cases.