Google Interview Prep: A 30-Day Plan That Actually Works
You just got an email from a Google recruiter. Your technical interview is in 30 days.
Panic is natural. But 30 days is enough time—if you spend it wisely.
This plan prioritizes what Google actually tests, not what feels productive. Every hour counts.
Before You Start: The Google Format
Google typically runs 4-5 technical interviews:
| Round | Duration | Focus |
|---|---|---|
| Phone Screen | 45 min | 1-2 coding problems |
| Onsite 1 | 45 min | Coding + data structures |
| Onsite 2 | 45 min | Coding + algorithms |
| Onsite 3 | 45 min | System design (L4+) |
| Onsite 4 | 45 min | Behavioral + Googleyness |
For L3-L4 roles, expect 70% coding, 20% system design, 10% behavioral. This plan reflects that ratio.
Week 1: Foundation & Pattern Recognition
Goal: Master the 5 highest-frequency patterns at Google
Daily schedule: 3-4 hours
Day 1-2: Arrays & Hashing
Google loves problems where hash maps optimize brute force.
Must-solve problems:
- Two Sum
- Group Anagrams
- Top K Frequent Elements
- Product of Array Except Self
- Encode and Decode Strings
Pattern to internalize: When you see "find pairs" or "group by property," think hash maps.
Day 3-4: Two Pointers
Almost every array problem has a two-pointer optimization.
Must-solve problems:
- Valid Palindrome
- 3Sum
- Container With Most Water
- Trapping Rain Water
Pattern to internalize: Sorted arrays + optimization = two pointers.
Day 5-6: Sliding Window
Google asks these constantly for string manipulation.
Must-solve problems:
- Longest Substring Without Repeating Characters
- Minimum Window Substring
- Longest Repeating Character Replacement
- Permutation in String
Pattern to internalize: "Contiguous subarray/substring" = sliding window.
Day 7: Review & Integration
- Re-solve 3 problems from this week without hints
- Write down the pattern for each
- Note which problems felt hard
Week 2: Trees, Graphs & Recursion
Goal: Handle the most common technical deep-dives
Daily schedule: 3-4 hours
Day 8-9: Binary Trees
Google interviewers love tree problems because they test recursion and edge cases.
Must-solve problems:
- Maximum Depth of Binary Tree
- Validate Binary Search Tree
- Lowest Common Ancestor
- Binary Tree Level Order Traversal
- Serialize and Deserialize Binary Tree
Pattern to internalize: Most tree problems are DFS with pre/in/post order or BFS with queues.
Day 10-11: Graphs (BFS/DFS)
Graph problems test your ability to model real-world scenarios.
Must-solve problems:
- Number of Islands
- Clone Graph
- Course Schedule (Topological Sort)
- Word Ladder
- Pacific Atlantic Water Flow
Pattern to internalize: "Connected components" = DFS. "Shortest path" = BFS. "Dependencies" = Topological sort.
Day 12-13: Backtracking
Combination problems are Google favorites.
Must-solve problems:
- Subsets
- Permutations
- Combination Sum
- Word Search
- N-Queens (understand, don't memorize)
Pattern to internalize: "Generate all possibilities" = backtracking with prune conditions.
Day 14: Review & Mock Interview
- Re-solve 4 problems from this week
- Do one 45-minute mock interview (time yourself strictly)
- Review what went wrong
Week 3: Dynamic Programming & Advanced Patterns
Goal: Build DP intuition and handle harder problems
Daily schedule: 4 hours
Day 15-16: 1D Dynamic Programming
DP is where many candidates struggle. Start simple.
Must-solve problems:
- Climbing Stairs
- House Robber
- Longest Increasing Subsequence
- Coin Change
- Word Break
Pattern to internalize: "Optimal substructure + overlapping subproblems" = DP. Start with recurrence relation, then optimize.
Day 17-18: 2D Dynamic Programming
These are rarer but appear in senior interviews.
Must-solve problems:
- Unique Paths
- Longest Common Subsequence
- Edit Distance
- Maximal Square
Pattern to internalize: Grid problems often have DP solutions where each cell depends on previous cells.
Day 19-20: Binary Search Variants
Google loves sneaky binary search applications.
Must-solve problems:
- Search in Rotated Sorted Array
- Find Minimum in Rotated Sorted Array
- Koko Eating Bananas
- Median of Two Sorted Arrays (if time permits)
Pattern to internalize: "Minimize the maximum" or "find threshold" = binary search on answer space.
Day 21: Full Mock Interview Day
- Do 2 back-to-back 45-minute mock interviews
- Simulate real interview conditions (no googling, time pressure)
- Debrief: Where did you get stuck? Communication issues?
Week 4: System Design, Behavioral & Final Push
Goal: Round out your preparation and polish performance
Daily schedule: 4-5 hours
Day 22-23: System Design (L4+)
Google system design focuses on scalability and trade-offs.
Must-study systems:
- URL Shortener (classic, covers basics)
- Design Twitter Feed
- Design Google Drive / Dropbox
- Design a Rate Limiter
Key concepts to know:
- Load balancing
- Database sharding
- Caching (Redis, CDN)
- Message queues
- CAP theorem
Day 24: Behavioral Prep
Google's "Googleyness" round matters more than you think.
Prepare stories for:
- A time you faced ambiguity
- A time you disagreed with a teammate
- A project you're proud of
- A time you failed and learned
Use the STAR format: Situation, Task, Action, Result.
Day 25-26: Weak Spot Intensive
Look at your notes from the past 3 weeks:
- Which patterns felt hardest?
- Which problems took the longest?
- Where did mock interviews expose gaps?
Spend these 2 days drilling your weaknesses.
Day 27-28: Full Interview Simulations
- Day 27: 2 coding interviews + 1 behavioral (simulate onsite)
- Day 28: 1 coding + 1 system design + 1 behavioral
Strict conditions: No breaks, no hints, 45 minutes each.
Day 29: Light Review
- Review your notes and patterns
- Walk through 5-6 problems mentally (no coding)
- Prepare your setup (IDE, whiteboard, camera)
- Get good sleep
Day 30: Interview Day
- Light breakfast
- Review your behavioral stories one more time
- Trust your preparation
The Problems That Matter Most
Based on Google interview data, these 20 problems appear most frequently:
| Priority | Problem | Pattern |
|---|---|---|
| 1 | Two Sum | Hash Map |
| 2 | Number of Islands | Graph DFS |
| 3 | LRU Cache | Design + Hash + DLL |
| 4 | Merge Intervals | Sorting + Sweep |
| 5 | Word Break | DP |
| 6 | Valid Parentheses | Stack |
| 7 | Binary Tree Level Order Traversal | BFS |
| 8 | Course Schedule | Topological Sort |
| 9 | Longest Substring Without Repeating | Sliding Window |
| 10 | 3Sum | Two Pointers |
| 11 | Serialize/Deserialize Binary Tree | Tree Traversal |
| 12 | Coin Change | DP |
| 13 | Trapping Rain Water | Two Pointers |
| 14 | Search in Rotated Sorted Array | Binary Search |
| 15 | Group Anagrams | Hash Map |
| 16 | Meeting Rooms II | Heap + Intervals |
| 17 | Clone Graph | Graph BFS/DFS |
| 18 | Maximum Subarray | Kadane's / DP |
| 19 | Validate Binary Search Tree | Tree DFS |
| 20 | Word Ladder | Graph BFS |
If you master these 20, you're prepared for 80% of what Google asks.
Common Mistakes to Avoid
Week 1 mistakes:
- Trying to solve everything in one sitting
- Not reviewing solved problems
- Skipping "easy" problems (they're not beneath you)
Week 2-3 mistakes:
- Memorizing solutions instead of patterns
- Not practicing under time pressure
- Ignoring communication practice
Week 4 mistakes:
- Cramming new problems instead of reviewing
- Skipping behavioral prep
- Not sleeping enough before the interview
How CodeSparring Accelerates This Plan
Every element of this plan maps to a CodeSparring feature:
| This Plan | CodeSparring Feature |
|---|---|
| Pattern recognition | 15 pattern-organized problem sets |
| Mock interviews | AI interviewer with Google-style follow-ups |
| Communication practice | Voice mode with real-time feedback |
| Review schedule | Automatic spaced repetition |
| Weakness tracking | Pattern mastery dashboard |
| Company-specific prep | Google interview scenarios |
You can do this plan with LeetCode and a stopwatch. But if you want simulated interviews with feedback, CodeSparring is built for exactly this use case.