DSA Interview Questions for Freshers: Top 30 Patterns with Solutions

Most coding interview questions are variations of 15-20 core patterns. If you recognize the pattern, you can solve any variation — even under pressure.

Companies like Amazon and Microsoft don't expect you to memorize 500 LeetCode problems. They expect you to recognize the pattern and apply it to a new problem in 30 minutes.

Two pointers — pair sum, three sum, container with most water. Start with sorted arrays, move pointers based on sum comparison.

Sliding window — maximum subarray sum K, longest substring without repeating characters. Maintain a window [left, right] and shrink/expand based on condition.

Prefix sum — range sum queries, equilibrium index. Precompute cumulative sums for O(1) range queries.

Kadane's algorithm — maximum subarray sum. Track current max and global max as you iterate.

Dutch national flag — sort 0s, 1s, 2s in-place. Three-way partitioning.

Hash map counting — character frequency, anagram check. Use Map or object for O(n) lookups.

Palindrome — expand from center, or reverse and compare. Two-pointer approach from both ends.

String matching — KMP algorithm, Rabin-Karp. Know at least one efficient string search algorithm.

Anagram grouping — sort each string as key, group by sorted key.

BFS / DFS — tree traversal, graph traversal. Use queue for BFS, stack/recursion for DFS.

Binary search tree — search, insert, delete. Know the BST property and in-order traversal.

Tree DP — diameter of binary tree, maximum path sum. Post-order traversal with return values.

Graph shortest path — Dijkstra for weighted, BFS for unweighted. Know when to use each.

Topological sort — course schedule, task dependency. Use DFS or Kahn's algorithm (BFS-based).

1D DP — Fibonacci, climbing stairs, house robber. Identify subproblems and overlapping computations.

2D DP — longest common subsequence, edit distance, 0/1 knapsack. Build a table from base cases.

DP on arrays — maximum subarray, jump game. Track state at each position.

DP on strings — longest palindromic substring, word break. Process substrings from shortest to longest.

Bitmask DP — traveling salesman, subset sum. Use bitmasks when state includes which elements are used.

Fast/slow pointers — detect cycle, find middle, merge point. Floyd's algorithm.

Reverse linked list — iterative and recursive. Fundamental operation tested everywhere.

Merge sorted lists — two-pointer merge. Extension: merge K sorted lists with heap.

Monotonic stack — next greater element, largest rectangle in histogram. Maintain a stack of indices.

Valid parentheses — stack-based matching. Extension: generate all valid parentheses combinations.

TCS / Wipro / Cognizant: Easy/medium arrays, strings, basic sorting. Check TCS coding questions on Apply PYQs.

Amazon / Microsoft: Medium arrays, trees, graphs, DP. 2-3 problems in OA. Check Amazon OA questions on Apply.

Google / Meta: Hard problems, often 2 patterns combined. System design may accompany coding.

Goldman Sachs / JP Morgan: Medium DP + array problems. Focus on correctness over optimization.

Start with NeetCode Blind 75 — covers all 15 core patterns with video explanations.

Practice on LeetCode with company tags — filter by your target company.

Solve under timed conditions: 30 minutes for easy, 45 for medium, 60 for hard.

Keep a pattern notebook: write the pattern name, approach, and time complexity for each problem.

Use Apply's company PYQs at /pyqs to see exactly which DSA problems each company asked in previous years.

DSA clears the coding round. The interview round tests communication, project knowledge, and behavioral fit.

Practice with Apply's AI mock interview at /mock-interview — it simulates real interview conditions with voice questions and scored feedback.