LeetCode Interview Preparation Guide: The 14-Pattern Approach
What LeetCode Actually Tests (It Is Not Memorization)
Companies that use LeetCode-style problems are not testing whether you have memorized 500 solutions. They are testing pattern recognition, problem decomposition, and the ability to communicate trade-offs under time pressure. The engineers who score highest on these interviews practice fewer problems more deliberately — not more problems superficially.
The 14 Patterns That Cover 90% of LeetCode Problems
Most LeetCode problems are variations of a small set of patterns. Once you recognize the pattern, the solution structure becomes obvious:
| Pattern | When to use | Example problems |
|---|---|---|
| Two Pointers | Sorted arrays, palindromes, sum targets | Two Sum II, Valid Palindrome, 3Sum |
| Sliding Window | Subarrays, substrings with constraints | Longest Substring Without Repeating, Minimum Window Substring |
| Fast & Slow Pointers | Cycle detection, midpoint finding | Linked List Cycle, Find Middle of Linked List |
| Binary Search | Sorted arrays, search space reduction | Search in Rotated Sorted Array, Find Peak Element |
| BFS / Level Order | Shortest path, tree levels | Binary Tree Level Order, Word Ladder |
| DFS / Backtracking | All combinations, permutations, paths | Subsets, Permutations, N-Queens |
| Dynamic Programming | Optimal substructure, overlapping subproblems | Climbing Stairs, Coin Change, Longest Common Subsequence |
| Merge Intervals | Overlapping ranges | Merge Intervals, Insert Interval, Meeting Rooms |
| Cyclic Sort | Arrays with values 1–N | Find All Missing Numbers, Find the Duplicate |
| Top K Elements | Kth largest/smallest, frequent elements | Kth Largest in Stream, Top K Frequent Elements |
| Monotonic Stack | Next greater/smaller element, span problems | Daily Temperatures, Largest Rectangle in Histogram |
| Trie | Prefix matching, word search | Implement Trie, Word Search II |
| Union-Find | Connectivity, grouping | Number of Islands, Redundant Connection |
| Heap / Priority Queue | Streaming minimums/maximums, scheduling | Merge K Sorted Lists, Task Scheduler |
The LeetCode Study Plan That Works (8 Weeks)
Weeks 1–2: Foundations (Arrays, Strings, HashMaps)
Do 3–4 Easy problems per day. Goal: write correct brute-force solutions quickly. Do not optimize yet — get comfortable translating a problem into code.
Problem set: Two Sum, Valid Anagram, Contains Duplicate, Best Time to Buy and Sell Stock, Valid Palindrome, Reverse Linked List, Maximum Depth of Binary Tree.
Weeks 3–4: Core Patterns (Trees, Binary Search, Two Pointers)
2–3 Medium problems per day. For each problem, write the brute force first, then optimize. Identify which pattern applies before writing any code.
Weeks 5–6: Hard Patterns (DP, Graph Algorithms, Advanced Trees)
1–2 Medium/Hard problems per day. Focus on DP (bottom-up vs top-down), graph traversal (BFS/DFS), and advanced tree problems (BST operations, LCA).
Weeks 7–8: Mock Interviews and Company-Specific Problems
One timed mock interview per day (2 problems in 45 minutes). Review the company's tagged problems on LeetCode. Practice talking through your approach before coding.
How to Practice LeetCode Effectively
- Say your approach out loud before coding. Interviewers evaluate communication as much as code correctness.
- Write the brute force first. Then optimize. Never start with the optimal solution — show your thinking process.
- After solving, look at the top solution even if yours passed. The gap between your approach and the optimal one teaches the pattern.
- Review problems you got wrong after 3 days, then again after a week. Spaced repetition is faster than grinding the same 20 problems daily.
- Time yourself. If Easy takes more than 15 minutes or Medium takes more than 35, you need more pattern practice, not more new problems.
LeetCode for Beginners: Where to Start
If you are new to competitive programming, start with LeetCode's free "Blind 75" problem list — 75 problems that cover every major pattern. Then do NeetCode's roadmap (available free at neetcode.io), which groups problems by pattern with video explanations.
Do not start with Hard problems. 90% of FAANG interviews use Medium difficulty. Mastering Medium problems thoroughly is more valuable than attempting Hard problems without the pattern foundation.
Practice the Interview, Not Just the Code
Solving problems in silence does not prepare you for talking through your reasoning with an interviewer watching. AissenceAI's coding interview mode simulates a live coding interview — you code while the AI asks clarifying questions, challenges your approach, and scores your communication. It mirrors what happens in a real Google or Meta technical screen.
Try AissenceAI coding interview practice →
FAQ
How many LeetCode problems do I need to solve before interviews?
Quality over quantity. 75–150 problems solved deliberately — understanding every pattern — is better than 300 problems rushed. The Blind 75 list is a solid target for most mid-level roles.
Is LeetCode enough for FAANG interviews?
For the coding round, yes. FAANG also tests system design (separate prep) and behavioral interviews (STAR method). LeetCode only covers one-third of the loop.
Which LeetCode plan is worth paying for?
LeetCode Premium is worth it specifically for company-tagged questions (you can see which problems Google or Amazon has historically used) and for the mock interview feature. The free tier covers all patterns.
What language should I use on LeetCode?
The language you are most fluent in for the target role. Python for data/ML roles. Java or C++ for performance-sensitive backend. TypeScript/JavaScript for frontend. Do not switch languages mid-prep — fluency in one language beats basic proficiency in three.