DSA Patterns You MUST Know

Coding interviews are notoriously difficult, and trying to memorize hundreds of individual LeetCode questions is a recipe for failure. The secret to success lies in pattern recognition. Once you learn to spot the underlying pattern of a problem, you can solve it easily. Here are the core patterns you must master.

1. Two Pointers

Used for searching pairs in a sorted array or list. By moving two pointers (e.g. one from the start, one from the end) towards each other, you can reduce O(N^2) search times to O(N).

• Typical Problems: Pair with Target Sum, Valid Palindrome, 3Sum.

2. Sliding Window

Used to perform operations on a specific subarray or substring of a given size, or dynamically sized based on constraints.

• Typical Problems: Maximum Sum Subarray of Size K, Longest Substring with K Distinct Characters.

3. Fast and Slow Pointers

Also known as the Hare & Tortoise algorithm. Uses two pointers moving at different speeds to detect cycles or find midpoints in linked lists.

• Typical Problems: Linked List Cycle, Find the Duplicate Number, Middle of the Linked List.

4. Merge Intervals

An efficient pattern to deal with overlapping intervals. Very common in scheduling and calendar problems.

• Typical Problems: Merge Intervals, Insert Interval, Meeting Rooms.