"Service-based vs product-based company DSA preparation" is not a difficulty debate — it's a completely different test. The same word, "DSA," means an easy-medium HackerRank round at TCS and a graphs-plus-DP gauntlet at a product company. Prepare for the wrong one and you either over-study for a mass recruiter or walk into a product interview hopelessly under-prepared. This post draws the two-tier map, then gives service-company engineers a concrete plan to cross over.

What service companies (TCS, Infosys, Wipro) actually test

Mass recruiters hire in thousands, so their first filter is built for scale, not depth. The coding bar is real but shallow. The bigger gate is usually aptitude and verbal.

• Aptitude first. Quant, logical reasoning, and verbal ability eliminate more candidates than coding does. TCS NQT, Infosys, and Wipro all front-load this.
• Easy-to-easy-medium coding. Arrays, strings, basic math, simple recursion, pattern printing. Think HackerRank-style implementation, not LeetCode Hard.
• Output and pseudocode rounds. Predict-the-output, fix-the-bug, and pseudocode MCQs reward C/C++/Java fundamentals over clever algorithms.

If a service company is your target, your DSA energy belongs in Tier 1 topics done flawlessly, not in segment trees. Arrays, strings, hashing, two pointers, basic recursion, and time-complexity intuition cover almost everything you'll be coding.

What product companies (and FAANG) demand instead

Product companies hire fewer people for higher leverage, so the bar moves from "can you code" to "can you model and optimise." Aptitude mostly disappears; intermediate-to-hard DSA takes its place.

• Graphs — BFS, DFS, topological sort, shortest paths. Near-mandatory at the product tier, near-absent at service.
• Dynamic programming — the 1D/2D classics, then DP-on-grids and subsequences.
• Backtracking and bit manipulation — permutations, subsets, and the bit tricks that service rounds never touch.
• Optimal complexity expected. A brute-force pass that clears TCS gets rejected at a product company — they want the O(n) or O(n log n).

The two-tier prep map

Dimension	Service (TCS / Infosys / Wipro)	Product / FAANG
Coding difficulty	Easy – easy-medium	Medium – hard
Aptitude weight	High (often decisive)	Low to none
Must-know topics	Arrays, strings, hashing, basic recursion	+ Graphs, DP, backtracking, bit-manip
What's optional	Graphs, DP, advanced trees	Pattern printing, pseudocode MCQs
Rounds	Aptitude, coding, HR	2–4 DSA rounds, system design, HR

If you're targeting service companies right now

Don't over-engineer. Lock down Tier 1 topics until they're automatic, drill aptitude in parallel, and practise writing clean, compiling code under a timer. You do not need graphs or DP to clear TCS — spending months there is misallocated effort. A focused four-to-six weeks on fundamentals plus aptitude is usually enough.

The switch roadmap: service engineer to product company

Already placed at a service company and want to jump? You have the discipline; you're missing the depth tier. Here's the sequence I'd run:

1. Weeks 1–2: re-solidify the base. Don't assume your aptitude-era coding holds. Re-grind arrays, strings, hashing, and two pointers at medium difficulty until pattern recognition is fast.
2. Weeks 3–5: trees and recursion depth. Traversals, BST operations, and recursion-on-trees are the on-ramp to everything harder. Skip this and graphs feel impossible.
3. Weeks 6–9: graphs and DP — the real gate. This is where product offers are won. BFS/DFS, topological sort, shortest paths, then the canonical DP patterns. Go slow and deep here.
4. Weeks 10–12: backtracking, bit-manip, and mocks. Fill the remaining gaps, then run timed mocks where you narrate your approach out loud.

For a fuller timeline you can adapt to your evenings-and-weekends reality, see the 90-day placement plan — compress the early phases since you already code daily, and spend the saved time on graphs and DP.

How SUITS handles both tiers

This is exactly the problem SUITS is built for. The same ~370 curated problems (Apna College, Love Babbar 450, Striver A2Z) get reordered by the company tier and role you're aiming at. Pick the service-ready subset — fundamentals first, no graph/DP detours — when TCS season is on. Flip to the product-ready deep set when you're chasing the switch, and graphs, DP, and backtracking move to the front. One progress model, two completely different prep paths, no spreadsheet. Set your target and start free.