Coding Interview Prep Guide: LeetCode Strategy, DSA, and Timelines
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Coding interviews are a learnable skill. The same categories of problems appear repeatedly across companies. Deliberate practice on a focused problem set produces better outcomes than grinding every problem on LeetCode. Spending three months on a structured preparation plan will outperform six months of unfocused practice.
What Coding Interviews Actually Test
Most technical screening questions fall into these categories, in approximate order of frequency:
| Category | Examples |
|---|---|
| Arrays and strings | Two pointers, sliding window, prefix sums |
| Hash maps and sets | Two sum, anagram detection, frequency counting |
| Linked lists | Reversal, cycle detection, merge sorted lists |
| Stacks and queues | Valid parentheses, monotonic stack, BFS/DFS |
| Trees | Binary tree traversal, BST operations, lowest common ancestor |
| Graphs | BFS, DFS, cycle detection, connected components |
| Dynamic programming | Fibonacci, knapsack, longest common subsequence |
| Binary search | Search in sorted array, rotated array, binary search on answer |
| Recursion and backtracking | Permutations, combinations, Sudoku solver |
| Heaps and priority queues | Top-K elements, merge K sorted lists |
A Structured Prep Timeline
8-Week Plan (Typical for Mid-to-Large Company Prep)
Weeks 1–2: Foundations
- Arrays, strings, and hash maps.
- Focus on two-pointer and sliding window patterns.
- Complete 20 easy-level LeetCode problems in these categories.
Weeks 3–4: Core Data Structures
- Linked lists, stacks, queues, and trees.
- Binary tree traversals (inorder, preorder, postorder) until they are automatic.
- Complete 25 easy and medium problems mixed.
Weeks 5–6: Graphs and Dynamic Programming
- BFS and DFS on graphs, cycle detection, topological sort.
- DP starting with 1D (Fibonacci, house robber, climbing stairs), then 2D.
- Complete 20 medium problems.
Weeks 7–8: Integration and Mock Interviews
- Binary search and heaps.
- Full mock interviews using LeetCode’s interview mode or Pramp.
- Review past problems. Time yourself. Speak through solutions out loud.
3-month plan: extend each phase to add more depth on DP and graph topics. 4-week plan: focus only on the top 50 patterns with no DP.
Essential Problem Sets
Do not try to complete all 2,500+ LeetCode problems. Use curated sets:
| Set | Problems | Best Use |
|---|---|---|
| Blind 75 | 75 problems | The foundational set; solve all of these first |
| NeetCode 150 | 150 problems | Expanded set with better category coverage |
| NeetCode 250 | 250 problems | Full prep for FAANG-level interviews |
| Grind 75 | 75 problems | Algorithm-focused alternative to Blind 75 |
NeetCode.io provides free video explanations for all 150 NeetCode problems organized by pattern. This is the highest-ROI free resource for coding interview prep.
Data Structures You Must Know in Your Target Language
Before your interview, implement these from memory in your primary language:
- Stack (using array or linked list)
- Queue (using deque or circular buffer)
- Linked list with reversal and cycle detection
- Binary search (exact, lower bound, upper bound)
- BFS on a graph using a queue
- DFS on a graph using recursion and explicit stack
- Min heap / max heap (understand how to use your language’s priority queue)
- Trie (prefix tree): insert, search, prefix search
How to Practice Effectively
- Set a time limit: 20 minutes for easy problems, 35 minutes for medium, 50 for hard.
- If stuck after the time limit: look at the hint, NOT the full solution. Try to implement from the hint before looking at full code.
- Review solutions you could not solve: understand the pattern, not the specific answer.
- Do not redo random problems: organize practice by pattern. Randomize within a pattern category.
- Practice out loud: narrate your approach as you code. Interview performance degrades without verbal practice.
Mock Interviews
Solving problems alone does not prepare you for the social pressure of a live interview. Practice with:
- Pramp — free peer mock interviews matched by topic and level.
- Interviewing.io — paid mock interviews with FAANG engineers; provides written feedback.
- LeetCode interview mode — timed problem solving with submission tracking.
- A study partner — even a non-technical friend watching you explain your approach adds useful pressure.
Next Steps
- Software Developer Interview Preparation
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