LeetCode was HARD until I Learned these 15 Patterns

I have solved more than 1500 LeetCode problems, and if there is one thing I have learned, it’s this:

LeetCode is less about the number of problems you have solved and more about how many patterns you know.

Learning patterns enables you to solve a wide variety of problems in lesser time and helps you quickly identify the right approach to a problem you have never seen before.

In this article, I’ll walk you through the 15 most important patterns I learned that made my LeetCode journey lot less painful.

I’ll share when to use each pattern along with a sample problem and provide links to LeetCode problems you can practice to learn these patterns better.

1. Prefix Sum

Prefix Sum involves preprocessing an array to create a new array where each element at index i represents the sum of the array from the start up to i. This allows for efficient sum queries on subarrays.

Use this pattern when you need to perform multiple sum queries on a subarray or need to calculate cumulative sums.

Sample Problem:

Given an array nums, answer multiple queries about the sum of elements within a specific range [i, j].