Coding Interview Patterns You Must Know

Why Patterns Matter in 2025

According to Indeed's 2025 data, competition for tech roles remains fierce with fewer open positions. However, companies like Google and Meta report that candidates who demonstrate pattern recognition skills pass interviews at 2-3x the rate of those who don't. Most coding interview questions are variations of common patterns. Learning these patterns allows you to recognize problem types and apply proven solutions quickly.

The 15 Essential Patterns

1. Two Pointers

Use when dealing with sorted arrays or linked lists where you need to find pairs.

• Example: Find pairs that sum to target
• Time complexity: O(n)
• Common in: Array problems

2. Sliding Window

Use for finding subarrays or substrings with specific properties.

• Example: Longest substring without repeating characters
• Time complexity: O(n)
• Common in: String/array problems

3. Fast and Slow Pointers

Use for detecting cycles in linked lists or arrays.

• Example: Detect cycle in linked list
• Time complexity: O(n)
• Common in: Linked list problems

4. Merge Intervals

Use when dealing with overlapping intervals.

• Example: Merge overlapping meetings
• Time complexity: O(n log n)
• Common in: Scheduling problems

5. Binary Search

Use on sorted arrays to find elements in O(log n).

• Example: Search in rotated sorted array
• Time complexity: O(log n)
• Common in: Search problems

6. BFS/DFS

Use for tree and graph traversal.

• BFS: Level-order traversal, shortest path
• DFS: Path finding, connected components
• Time complexity: O(V + E)

7. Dynamic Programming

Use for optimization problems with overlapping subproblems.

• Example: Longest common subsequence
• Key: Identify state and transitions
• Common in: Optimization problems

8. Backtracking

Use for generating all combinations or permutations.

• Example: Generate all valid parentheses
• Key: Prune invalid paths early
• Common in: Combination problems

How to Practice

1. Learn one pattern at a time
2. Solve 5-10 problems for each pattern
3. Identify the pattern before solving
4. Write clean, readable code
5. Analyze time and space complexity

Resources

• LeetCode problem lists by pattern
• Grokking the Coding Interview
• Blind 75 curated list
• NeetCode roadmap

Conclusion

Mastering these patterns transforms coding interviews from guesswork to systematic problem-solving. Focus on understanding when to apply each pattern.