How to Prepare for a Coding Interview: The Complete LeetCode Study Plan

Most engineers approach LeetCode wrong. They grind 300+ problems randomly, burn out, and walk into interviews unable to recognize patterns under pressure. This guide shows you the smarter approach.

The Core Insight: Patterns Over Problems

There are ~2,000+ LeetCode problems. You cannot solve them all. You don't need to.

There are approximately 15 core patterns that cover 80% of all interview problems. Learn the patterns, and you can solve problems you've never seen before.

The 15 patterns:

1. Two pointers
2. Sliding window
3. Fast and slow pointers
4. Merge intervals
5. Cyclic sort
6. In-place linked list reversal
7. Tree BFS
8. Tree DFS
9. Two heaps
10. Subsets / backtracking
11. Modified binary search
12. Bitwise XOR
13. Top-K elements
14. K-way merge
15. Dynamic programming (several sub-patterns)

The Recommended Study Order

Phase 1: Foundations (3 weeks)

Start with arrays and strings — 60–70% of all interview problems involve them at some level.

• Arrays: two pointers, sliding window, prefix sums
• Strings: palindromes, anagrams, character frequency
• Hashmaps: frequency counting, two-sum pattern
• Stacks and queues: monotonic stack, BFS

Target: 5 problems/day, easy to medium. Aim for < 25 minutes per easy, < 40 minutes per medium.

Phase 2: Core Data Structures (3 weeks)

• Linked lists: reversal, cycle detection (Floyd's), merge
• Trees: DFS (preorder/inorder/postorder), BFS (level order), BST operations
• Heaps: top-K, merge K sorted lists, median of stream
• Graphs: DFS, BFS, topological sort, union-find

Target: 4–5 problems/day, medium focus.

Phase 3: Advanced Patterns (2 weeks)

• Dynamic programming: Fibonacci, 0/1 knapsack, longest common subsequence, intervals
• Backtracking: permutations, subsets, N-queens
• Binary search: rotated arrays, search on answer
• Tries: prefix search, word dictionary

Target: 3–4 problems/day, medium-hard.

Phase 4: Company-Specific Prep (2 weeks)

Filter LeetCode by company tag. Focus on problems asked in the last 6 months. Time yourself at 45 minutes per problem — this is the actual interview constraint.

The Blind 75 and NeetCode 150

Blind 75: A curated list of 75 problems covering all critical patterns. If you solve all 75 correctly and understand why each solution works, you can pass most FAANG phone screens.

NeetCode 150: Extends Blind 75 with harder problems and better pattern grouping. The NeetCode roadmap on YouTube explains each pattern clearly.

Recommendation: Complete the Blind 75 first. If your target companies are Google/Meta/Amazon, extend to NeetCode 150.

How to Actually Practice (Not Just Grind)

The 3-pass method:

Pass 1 (Attempt): Try the problem for 20–25 minutes without hints. If you solve it — great. If you're stuck, write down what you tried and why it failed.

Pass 2 (Learn): Look at the optimal solution. Understand every line — not just the approach, but why that data structure, why that index, why that loop bound. Don't move on until you can explain it out loud.

Pass 3 (Reinforce): 3–5 days later, re-solve the problem without looking at your previous solution. This is the step most people skip — it's also the most important for retention.

Common Mistakes to Avoid

Mistake 1: Solving problems without talking out loud Interviews require you to narrate your thinking. Practice out loud from day one. It feels awkward. Do it anyway.

Mistake 2: Moving on after passing the test cases Before declaring a solution done: analyze time and space complexity, check edge cases (empty array, single element, negatives, duplicates, integer overflow), and ask "can I do better?"

Mistake 3: Grinding hard problems too early Hard problems before you've mastered the patterns causes frustration and teaches you nothing. Do mediums until they feel comfortable, then add hards.

Mistake 4: Never doing mock interviews Solving problems in your IDE at your own pace is very different from solving them in 45 minutes in a shared editor while someone watches. Do at least 5 timed mock interviews before your first real interview.

Tracking Your Progress

Keep a simple log:

• Problem name, difficulty, date
• Did you solve it independently? (Y/N)
• Time taken
• Pattern used
• Key insight (1 sentence)

Review your log weekly. Patterns you're consistently slow on need more reps.

Building the Habit

2 hours/day, 5 days/week = 10 hours/week. Over 8 weeks, that's 80 hours of focused practice — enough to be ready for most FAANG phone screens and oncites.

The candidates who succeed aren't solving 5+ hours a day. They're solving consistently for 2 hours, reflecting on every problem, and doing mock interviews regularly.

Use CareerLift.ai for mock interview sessions where you can practice coding walkthrough explanations and get real-time feedback on how you explain your solutions — the part that most LeetCode practice doesn't cover.