Which questions to solve on LeetCode?

When preparing for coding interviews on LeetCode, it's essential to focus on a mix of problem types that reflect the most commonly tested concepts. Here's a guide on which types of problems you should solve based on the type of interview you're preparing for:

1. Arrays and Strings

These are foundational topics, and you'll encounter these in almost every coding interview.

• Example Questions:
  • "Two Sum"
  • "Longest Substring Without Repeating Characters"
  • "Merge Intervals"

2. Linked Lists

Linked lists are frequently tested because they assess understanding of pointers and memory management.

• Example Questions:
  • "Reverse Linked List"
  • "Merge Two Sorted Lists"
  • "Detect Cycle in a Linked List"

3. Trees and Binary Search Trees (BST)

Tree-based problems often appear in interviews because they test recursive thinking and traversal techniques.

• Example Questions:
  • "Binary Tree Inorder Traversal"
  • "Lowest Common Ancestor of a Binary Search Tree"
  • "Serialize and Deserialize Binary Tree"

4. Dynamic Programming

Dynamic programming (DP) is a crucial topic for intermediate and advanced interviews, testing your ability to optimize algorithms.

• Example Questions:
  • "Climbing Stairs"
  • "Longest Increasing Subsequence"
  • "House Robber"

5. Graphs

Graph problems are commonly seen in tech interviews for companies like Google and Amazon. They test understanding of algorithms like BFS (Breadth-First Search) and DFS (Depth-First Search).

• Example Questions:
  • "Number of Islands"
  • "Clone Graph"
  • "Course Schedule"

6. Recursion and Backtracking

These types of problems often involve searching for solutions in a complex space and are great for practicing logical reasoning.

• Example Questions:
  • "Subsets"
  • "Permutations"
  • "N-Queens"

7. Sorting and Searching

Sorting and searching algorithms are essential for optimizing code, and interviewers frequently test these to see how well candidates can implement and improve efficiency.

• Example Questions:
  • "Kth Largest Element in an Array"
  • "Search in Rotated Sorted Array"
  • "Merge Sorted Array"

8. Hash Maps and Hash Sets

These problems are important for understanding efficient data retrieval and avoiding duplicate values.

• Example Questions:
  • "Valid Anagram"
  • "Group Anagrams"
  • "Two Sum" (using a hash map for optimization)

9. Bit Manipulation

Although not as commonly asked, bit manipulation problems often appear in interviews for their ability to test low-level data processing skills.

• Example Questions:
  • "Single Number"
  • "Number of 1 Bits"
  • "Reverse Bits"

10. System Design (for Senior Candidates)

While not directly on LeetCode, understanding system design is crucial for senior roles. After solving basic coding problems, focus on Grokking the System Design Interview or LeetCode’s System Design Questions for more advanced prep.

How to Approach LeetCode Problems

• Start with Easy/Medium problems: Focus on building a solid foundation by solving basic problems in each category. For example, "Two Sum" and "Climbing Stairs" are great starters.
• Follow coding patterns: Use resources like Grokking the Coding Interview to recognize common patterns that will help solve similar problems faster.
• Progress to Medium/Hard problems: Once you're comfortable with easy problems, move to more challenging ones, such as dynamic programming and advanced tree/graph problems.

Conclusion

To maximize your interview success on LeetCode, focus on key topics like arrays, linked lists, dynamic programming, graphs, and system design. Make use of resources like LeetCode Explore and Grokking the Coding Interview for structured preparation. Consistent practice across a range of difficulty levels will help you build the confidence and problem-solving skills needed for tech interviews.