In today’s competitive tech job market, LeetCode has become the go-to platform for preparing for coding interviews.

The “Top Interview 150” list on LeetCode is a curated collection of problems that frequently appear in technical interviews at top companies like Google, Amazon, Facebook, Apple, and Microsoft.

In this blog post, we’ll break down this list and provide strategies to help you master these essential problems.

Why the Top Interview 150 Matters

The Top Interview 150 isn’t just a random assortment of problems—it’s a carefully selected set that covers:

1. Frequency: These are the most commonly asked questions in real interviews
2. Diversity: They cover all major data structures and algorithms
3. Difficulty: They range from easy to hard, matching actual interview difficulty
4. Patterns: They represent common problem-solving patterns you need to know

Breakdown of Problem Categories

Let’s examine the distribution of problems in the Top Interview 150:

1. Arrays & Hashing (26 problems)
– Two Sum
– Contains Duplicate
– Product of Array Except Self
– Valid Sudoku
– And many more…

Key Concepts: Hash maps, sliding window, prefix sums, in-place operations

2. Two Pointers (10 problems)
– Valid Palindrome
– 3Sum
– Container With Most Water
– Trapping Rain Water

Key Concepts: Pointer manipulation, sorting prerequisites, boundary conditions

3. Sliding Window (7 problems)
– Best Time to Buy and Sell Stock
– Longest Substring Without Repeating Characters
– Minimum Window Substring

Key Concepts: Window expansion/contraction, hash map tracking

4. Stack (8 problems)
– Valid Parentheses
– Evaluate Reverse Polish Notation
– Min Stack

Key Concepts: LIFO principle, monotonic stacks, recursion simulation

5. Binary Search (7 problems)
– Search in Rotated Sorted Array
– Find Minimum in Rotated Sorted Array
– Median of Two Sorted Arrays

Key Concepts: Search space reduction, boundary conditions

6. Linked Lists (11 problems)
– Reverse Linked List
– Merge Two Sorted Lists
– Linked List Cycle
– LRU Cache

Key Concepts: Pointer manipulation, dummy nodes, fast/slow pointers

7. Trees (17 problems)
– Invert Binary Tree
– Validate Binary Search Tree
– Binary Tree Level Order Traversal
– Serialize and Deserialize Binary Tree

Key Concepts: Recursion, DFS/BFS, tree properties

8. Tries (3 problems)
– Implement Trie
– Word Search II

Key Concepts: Prefix trees, backtracking

9. Heap/Priority Queue (6 problems)
– Kth Largest Element in an Array
– Merge k Sorted Lists
– Find Median from Data Stream

Key Concepts: Min/max heaps, streaming data

10. Backtracking (8 problems)
– Subsets
– Combination Sum
– Word Search
– N-Queens

Key Concepts: Recursive exploration, pruning, state management

11. Graphs (13 problems)
– Number of Islands
– Clone Graph
– Course Schedule
– Word Ladder

Key Concepts: DFS/BFS, topological sort, union find

12. Advanced Graphs (6 problems)
– Alien Dictionary
– Graph Valid Tree

Key Concepts: Complex graph properties, advanced algorithms

13. 1D Dynamic Programming (17 problems)
– Climbing Stairs
– House Robber
– Coin Change
– Longest Increasing Subsequence

Key Concepts: State definition, recurrence relations, optimization

14. Bit Manipulation (5 problems)
– Number of 1 Bits
– Reverse Bits
– Missing Number

Key Concepts: Bitwise operations, XOR properties

Study Strategies for the Top Interview 150

1. Categorize Before You Solve
Group problems by their patterns before solving them. This helps you recognize similarities between new problems and ones you’ve already solved.

2. Master the Fundamentals First
Before jumping into problems, ensure you understand:
– Time and space complexity analysis
– How each data structure works internally
– Common algorithm paradigms

3. Follow the 3-Step Problem Solving Approach
For each problem:
1. Understand: Restate the problem in your own words
2. Plan: Develop an approach before coding
3. Implement & Test: Write code and verify with test cases

4. Time Yourself
Simulate real interview conditions by timing your problem-solving sessions (30-45 minutes per problem).

5. Spaced Repetition
Revisit problems after increasing intervals to reinforce your understanding.

6. Focus on Patterns, Not Memorization
Understand why solutions work rather than memorizing code. Common patterns include:
– Two pointers
– Sliding window
– Prefix sum
– BFS/DFS
– Dynamic programming

Recommended Study Plan

Week 1-2: Arrays, Strings, and Hashing
– Focus on basic data structure manipulation
– Master hash map applications

Week 3-4: Pointers, Linked Lists, Stacks
– Develop pointer manipulation skills
– Understand stack applications

Week 5-6: Trees, Graphs, Recursion
– Master tree traversals
– Understand graph representations

Week 7-8: Dynamic Programming
– Start with 1D DP problems
– Understand state transition

Week 9-10: Advanced Topics
– Tackle harder problems in each category
– Focus on your weak areas

Common Pitfalls to Avoid

1. Jumping to code too quickly: Take time to understand and plan
2. Neglecting edge cases: Always consider empty inputs, single elements, etc.
3. Ignoring time/space complexity: Be prepared to discuss optimizations
4. Only solving once: Revisit problems to reinforce learning
5. Avoiding hard problems: Challenge yourself with difficult questions

Resources to Supplement Your Learning

1. LeetCode’s discussion boards
2. NeetCode.io (video explanations)
3. “Cracking the Coding Interview” book
4. “Algorithms” by Robert Sedgewick (for deeper understanding)
5. “Elements of Programming Interviews” (for advanced problems)

Conclusion

The Top Interview 150 on LeetCode represents a comprehensive collection of problems that cover nearly all concepts tested in technical interviews. By systematically working through these problems, understanding the underlying patterns, and practicing under timed conditions, you’ll significantly improve your chances of success in coding interviews.

Remember, consistency is key—regular practice over time yields better results than cramming. Start with easier problems to build confidence, then gradually tackle more challenging ones.

With dedication and the right approach, you’ll be well-prepared to tackle any coding interview that comes your way!

Happy coding, and best of luck with your interview preparation!