You might have solved dozens of LeetCode problems. You might be familiar with techniques like sliding window, binary search, or BFS. And yet, when you open a new problem, the first question often is: “Which approach fits here?”

That moment highlights a common challenge. Understanding a pattern on its own is different from recognizing when to use it, especially under time pressure and without guidance.

This chapter focuses on that gap. Instead of introducing new patterns, we will work on identifying the right one for a given problem. We will look at three practical signals: the input type, the constraints, and the keywords in the problem statement. The goal is to build a simple, repeatable way to narrow down the approach for any problem.