1582 articles
LeetCode 125 Valid Palindrome is the most common two pointer warm-up at Meta, Microsoft, and Amazon. Learn the inward-converging pointer technique that runs in O(n) time and O(1) space without building a cleaned copy of the string.
LeetCode 344 Reverse String is the simplest two pointer swap problem and a daily warm-up at Amazon, Apple, and Meta. Solve it in O(n) time and O(1) space using opposite-end pointers without allocating a new array.
LeetCode 977 Squares of a Sorted Array is a classic Google and Bloomberg two pointer question. Squaring negatives flips the sort order, so we merge from the outside in to produce a sorted output in O(n) time without re-sorting.
LeetCode 27 Remove Element introduces the fast and slow pointer pattern used in dozens of in-place array problems. Master the read and write index template here and LC 26, LC 283, and LC 80 become trivial.
LeetCode 26 Remove Duplicates from Sorted Array is the canonical fast and slow pointer deduplication problem. Microsoft, Meta, and Amazon use it to verify that candidates can compare against the previous kept element in O(n) time and O(1) space.