Two Pointers Pattern: 5 Problems, Python And Java

One DSA pattern, taught properly instead of listed. You get the five signals that tell you a question is a two-pointer question, the three shapes it comes in — opposite ends converging, fast and slow, and two lists at once — with a clean Python and Java template for each, then five problems worked end to end: Two Sum on a sorted array, valid palindrome, remove duplicates in place, container with most water and 3Sum. Every problem has the naive cost, the insight, running code in both languages, a hand trace of a small input and the complexity, and the guide closes with the four mistakes that quietly break the pattern. 14 pages, PDF.