15 Essential Coding Interview Patterns to Solve 100+ LeetCode Problems

15 Coding Interview Patterns to Solve Coding Problems on Interviews

image_credit — Educative.io

Hello guys, Happy New Year. If you have prepared for coding interviews then you know how daunting it can be. Apart from the regular work you do, you need to spend a considerable amount of time practicing data structure and algorithms problems just for the interview.

I have done that, but more often than not, it’s either miss or hit.

If you get the coding problem you have practiced then the interview can be a breeze, all you need to do is act as if you are solving that question first time — but if you get a really unknown question, then good luck to you.

I knew my interview prep approach wasn’t foolproof and needed improvement.

After solving so many problems, I noticed certain tricks, or patterns, I could apply repeatedly — for example, how the Two-Pointer technique on a linked list can help find the middle element or detect any cycle.

I didn’t know that these are essential coding patterns until I came across course from DesignGurus.io. This course teaches you 24 coding patterns which can be used to solve thousands of LeetCode problems.

That’s the first time I came across this terminology and also learned many other patterns I didn’t even know.

Just knowing that helped me a lot in my coding interview prep and also to many of my readers who thanked and appreciated me that I told them about these patterns and this course.

In this article, I am going to share 15 essential coding interview patterns you can use to solve 100+ coding problems. Many of them are also covered in , in greater depth.

Now, you don’t need to blindly solve many coding problems just to get your hands on it. Instead, learn these patterns, and then start using them to solve problems.

To make your preparation structured and effective, I also recommend . This course covers more advanced coding patterns you need for interviews and integrates interactive practice.

Educative also just rolled out AI-powered . Think of it as a custom prep roadmap, tailored to your strengths and gaps.

15 Essential Coding Interview Patterns Every Software Developer Should Know

Without any further ado, here are the 15 essential coding patterns you should master, along with 2–3 Leetcode problems to practice for each.

1. Two Pointers

Two Pointers is a versatile pattern that involves using two pointers to traverse an array or linked list efficiently.

This was the first coding pattern I learned and it works remarkably well on solving linked list and array based problems like of the list or .

Key Concepts:

• Optimize problems involving pairs, such as sum or difference.
• Avoid nested loops to reduce time complexity.

LeetCode Problems:

1. Two Sum II — Input Array Is Sorted (167)
2. Remove Duplicates from Sorted Array (26)
3. Move Zeroes (283)

2. Prefix Sum

Prefix Sum is a powerful technique for optimizing range queries in arrays. By preprocessing cumulative sums, you can solve range-based problems efficiently.

This coding pattern is also very important for solving array based problems like Subarray Sum Equals K on Leetcode.

Key Concepts:

• Precompute cumulative sums for quick access.
• Use for range queries like subarray sums.

Leetcode Problems:

1. Range Sum Query — Immutable (303)
2. Subarray Sum Equals K (560)
3. Minimum Value to Get Positive Step by Step Sum (1413)

3. Sliding Window

Sliding Window is a powerful pattern to optimize problems involving contiguous subarrays. This problem can be tough to understand at first but once you solve a couple of problems, you will appreciate the simplicity of it.

Key Concepts:

• Maintain a window over part of the array.
• Expand or contract the window as needed.

Leetcode Problems:

1. Longest Substring Without Repeating Characters (3)
2. Maximum Sum of Subarray of Size K (643)
3. Minimum Window Substring (76)

4. Fast & Slow Pointers

Fast & Slow Pointers (also called the Floyd’s Cycle Detection) are commonly used for . This pattern is also known as tortoise and hare patttern.

Key Concepts:

• Use two pointers moving at different speeds.
• Detect cycles or meeting points in a sequence.

Leetcode Problems:

1. Linked List Cycle (141)
2. Find the Duplicate Number (287)
3. Happy Number (202)

5. LinkedList In-Place Reversal

This pattern focuses on reversing portions of a Linked List without extra space. In place algorithms can be used when you have memory constraint.

Key Concepts:

• Reverse a Linked List iteratively or recursively.
• Solve problems requiring sublist reversal.

LeetCode Problems:

1. (206)
2. (92)
3. Swap Nodes in Pairs (24)

6. Monotonic Stack

The Monotonic Stack is a structured stack that maintains elements in sorted order (increasing or decreasing).

Key Concepts:

• Solve problems involving the next greater or smaller element.

LeetCode Problems:

1. Daily Temperatures (739)
2. Next Greater Element I (496)
3. Largest Rectangle in Histogram (84)

7. Top ‘K’ Elements

This pattern focuses on efficiently finding the top K largest, smallest, or most frequent elements. You can use this pattern to solve problems like how to find the Kth largest element in a given array.

You can also find many questions based on these patterns on , where you will get a chance to solve 99 selected questions instead of 2800 Leetcode problems.

Key Concepts:

• Use heaps (priority queues) or sorting.

LeetCode Problems:

1. Top K Frequent Elements (347)
2. Kth Largest Element in an Array (215)
3. Find K Pairs with Smallest Sums (373)

8. Overlapping Intervals

This pattern involves merging or handling overlapping intervals in sorted order.

Key Concepts:

• Sort intervals and merge based on conditions.

LeetCode Problems:

1. Merge Intervals (56)
2. Insert Interval (57)
3. Meeting Rooms II (253)

9. Modified Binary Search

Modified Binary Search optimizes searching in sorted or rotated arrays.

Key Concepts:

• Apply binary search creatively for custom conditions.

LeetCode Problems:

1. Binary Search (704)
2. Search in Rotated Sorted Array (33)
3. Find Peak Element (162)

10. Binary Tree Traversal

This is not a pattern but an essential binary tree concept which is presented as a pattern. Basically you need to learn various traversal techniques such as in-order, pre-order, and post-order to solve tree problems.

Another key thing to remember is that with the in-order traversal you can print the list in a sorted order. Not many developers know this but it’s a very good thing to remember.

LeetCode Problems:

1. Binary Tree Inorder Traversal (94)
2. Maximum Depth of Binary Tree (104)

11. Depth-First Search (DFS)

DFS explores tree or graph nodes as deep as possible before backtracking. In other words, all the nodes in one branch are explored before starting another branch.

Leetcode Problems:

1. Path Sum (112)
2. Number of Islands (200)

12. Breadth-First Search (BFS)

BFS explores nodes level by level, often implemented with a queue. This pattern is used to solve binary tree related pattern and it also known as level order traversal because it traverse all nodes in one level before moving to the next level.

LeetCode Problems:

1. Binary Tree Level Order Traversal (102)

13. Matrix Traversal

Matrix Traversal involves navigating through 2D grids or matrices. As it says, this pattern is used heavily to solve any problem where data can be represented in matrix.

LeetCode Problems:

1. Flood Fill (733)

14. Backtracking

Backtracking solves problems recursively by trying all solutions and backtracking when needed.

LeetCode Problems:

1. Subset (78)

15. Dynamic Programming Patterns

Dynamic Programming focuses on breaking problems into subproblems and solving them optimally and you can develop patterns by solving problems like knapsack problem.

I also suggest you to go through on Educative to better understand these Dynamic programming patterns.

LeetCode Problems:

1. Climbing Stairs (70)
2. Longest Increasing Subsequence (300)

That’s it about 15 essential Coding Interview Patterns for interviews. You must master these 15 patterns if you want to crack the interview and get the offer you want.

I also encourage you to check out on Educative for interactive, in-depth explanations and real coding exercises.

And, if you prefer to read books then by Alex Xu and Shaun Gunawardane is another great book to learn coding interview patterns.

You will also learn 24 patterns there and then you can combine these patterns with consistent LeetCode practice, and you’ll be well-prepared to land your dream job!

Preparing for coding interviews can be daunting, but focusing on essential problem-solving and coding patterns can make it significantly easier.

Instead of learning solutions to individual problems, mastering these patterns will help you tackle various coding challenges effectively.

You can also start with , where you will get a chance to solve 99 selected questions instead of 2800 Leetcode problems. This will also help you to master the above coding patterns better.

Hopefully, this should be a good starting point for you.

Other System Design Tutorials and Resources you may like

• Is DesignGuru’s System Design Course worth it
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• 10 Best Places to Learn System Design in 2025
• My Favorite Software Design Courses for 2025
• 3 Places to Practice System Design Mock interviews
• Is Designing Data-intensive application book worth reading?

All the best for your Software Developer and CodingInterviews, if you have any doubts or questions, feel free to ask in the comments.

P. S. — If you struggle with System design and do well on coding interview then I also recommend you to and start learning System Design concepts, you will thank me later. Make it a goal for the new year and you will surely be a better Software Engineer.