DSA Plan for Backend Interviews

Goal of this file: Give you a focused DSA plan that maximizes ROI for backend interviews (no unnecessary topics).

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1. Topics Overview (Backend-Relevant Only)

Topic	Why It Matters for Backend
Arrays & Strings	Parsing requests, basic transformations, validation
Hash Maps & Sets	Caching, de-duplication, counting, indexing-like logic
Linked Lists	LRU cache, queues, streaming structures
Stacks & Queues	Request processing, parsing, BFS/DFS helpers
Trees	Hierarchical data (folders, comments), search
Graphs	Networks, dependency graphs, shortest paths
Heaps/Priority Queues	Scheduling, task prioritization, top-K queries
Two Pointers	Windowed processing on sorted/linear data
Sliding Window	Streaming analytics, rate limiting, rolling metrics

You don’t need dynamic programming mastery for most backend SDE-II roles; focus instead on these core patterns.

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2. Weekly Plan (16-Week Track)

This runs in parallel with other phases. See week-XX.md for daily allocations.

Weeks	Focus	Problems / Day
1–2	Arrays, strings, hash maps, sets	3
3–4	Two pointers, sliding window	3–4
5–6	Linked lists, stacks, queues	3
7–8	Trees (BST, generic)	3
9–10	Graphs (BFS/DFS, shortest path)	3
11–12	Heaps, top-K, scheduling-like problems	3
13–14	Mixed revision, timed practice	4
15–16	Mixed revision + company-style sets	4–5

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3. Pattern-Based Study Plan

Arrays & Strings

• Key Patterns

  • Frequency counting using hash maps.
  • Prefix sums (basic).
  • In-place modifications, two-pointer sweeps.

• Checklist

  • Can I:
    • Use a hash map for counting/lookup in (O(1)) average time?
    • Reason about off-by-one errors with indices?
    • Detect and handle Unicode/edge cases in strings (conceptually)?

Hash Maps & Sets

• Key Patterns

  • Detect duplicates.
  • Mapping from ID to object/metadata.
  • Grouping (e.g., by category or key).

• Checklist

  • Can I design an API that uses a map/set internally to support (O(1)) operations?

Two Pointers & Sliding Window

• Two Pointers

  • Sorted arrays merging, partitioning, removing elements in-place.

• Sliding Window

  • Longest/shortest subarray satisfying condition.
  • Maintaining counts or sums in a moving window.

• ASCII View

Array: [a, b, c, d, e, f]
Window (size 3) moves:
[a, b, c]      -> [b, c, d]      -> [c, d, e]      -> [d, e, f]
  l     r          l     r          l     r          l     r

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4. Recommended Problem Mix (Per Topic)

Replace "PlatformProblemName" with actual problem names from your preferred platform.

Topic	Easy	Medium	Notes
Arrays & Strings	5	10	Focus on frequency counting & subarrays
Hash Maps/Sets	5	10	Use maps for counting & indexing
Linked Lists	5	5	Reversal, middle, cycle detection
Trees	5	10	BFS/DFS, height, lowest common ancestor
Graphs	3	7	BFS/DFS, shortest path, topological sort
Heaps/PQ	3	7	Top-K, scheduling, merging sorted lists
Sliding Window	5	10	Longest/shortest subarray/window

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5. Daily Template (4-Hour and 6-Hour Days)

• 4-Hour Day DSA Block (Integrated with Other Topics)

  • Warm-up (10–15 min): 2–3 quick easy problems or reading old notes.
  • Focused practice (60–75 min): 2–3 new medium problems on 1 topic.
  • Review (10–15 min): Document patterns and mistakes.

• 6-Hour Day DSA Block

  • Same as above, but add:
    • 1 extra medium problem.
    • 1 timed problem (25–30 minutes).

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6. How to Review and Build Patterns

• After solving a problem:
  • Write 1–3 bullet points:
    • Which pattern did this use? (e.g., sliding window, BFS, heap).
    • What was the invariant you maintained?
    • What common pitfall did you avoid or fall into?
• Build a personal pattern cheat sheet:
  • Example sections: "Sliding Window", "Two Pointers", "Top-K with Heap", "Graph Traversal".

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7. Company-Focused Rounds (Weeks 15–16)

• Create sets of 2–3 problems that you solve in 75 minutes:
  • 1 array/hash map problem.
  • 1 tree/graph/heap problem.
  • 1 sliding window or two-pointer problem.
• After each set:
  • Grade yourself on:
    • Correctness (did you handle edge cases?).
    • Complexity (can you justify it?).
    • Communication (could an interviewer follow your reasoning?).