Interview Questions Bank: 50+ Curated Practice Questions by Category

A curated collection of 50+ interview questions organized by category with difficulty ratings, key concepts tested, and recommended approaches — designed for structured interview preparation.

What You’ll Learn

• 50+ categorized interview questions with difficulty ratings
• Key concepts tested by each question
• Recommended approaches and common pitfalls
• How to structure your preparation across categories
• Questions for coding, system design, and behavioral rounds

Why This Question Bank Matters

Random practice is inefficient. When you solve problems without a system, you miss categories, over-practice easy problems, and arrive at interviews unprepared for the specific question types your target company asks. This bank is organized by category and difficulty so you can practice systematically, track your coverage, and focus on weak areas.

DodaTech interviewers use questions similar to these when evaluating candidates for Doda Browser and Durga Antivirus Pro engineering roles.

Learning Path

    flowchart LR
  A[Data Structures Deep] --> B[Algorithms Deep]
  B --> C[Question Bank<br/>You are here]
  C --> D[Mock Interviews]
  D --> E[Negotiation Guide]
  style C fill:#f90,color:#fff
  

Arrays and Strings

Easy

Medium

Hard

Example Solution: Two Sum

def two_sum(nums, target):
    """
    Given an array of integers, return indices of two numbers
    that add up to target.
    Time: O(n), Space: O(n)
    """
    seen = {}
    for i, num in enumerate(nums):
        complement = target - num
        if complement in seen:
            return [seen[complement], i]
        seen[num] = i
    return []

Linked Lists

Trees

Example Solution: Validate BST

def is_valid_bst(root):
    """
    Determine if a binary tree is a valid BST.
    Each node's value must be within a valid range.
    Time: O(n), Space: O(h) where h is tree height.
    """
    def validate(node, low, high):
        if not node:
            return True
        if not (low < node.val < high):
            return False
        return (validate(node.left, low, node.val) and
                validate(node.right, node.val, high))

    return validate(root, float('-inf'), float('inf'))

Graphs

Dynamic Programming

Example Solution: Coin Change

def coin_change(coins, amount):
    """
    Find minimum number of coins to make amount.
    If impossible, return -1.
    Time: O(amount * len(coins)), Space: O(amount)
    """
    dp = [float('inf')] * (amount + 1)
    dp[0] = 0
    for coin in coins:
        for a in range(coin, amount + 1):
            dp[a] = min(dp[a], dp[a - coin] + 1)
    return dp[amount] if dp[amount] != float('inf') else -1

System Design

Example: URL Shortener Design

1. Generate short key (Base62 encoding of ID, or hash)
2. Store mapping in distributed database (Cassandra/DynamoDB)
3. Cache popular URLs (Redis)
4. Use consistent hashing to distribute keys
5. Rate limit per user to prevent abuse
6. Analytics: track clicks per short URL

Behavioral Questions

Frontend-Specific

Preparation Strategy

12-Week Plan

Weeks 1-2: Arrays, Strings, Hash Maps (questions 1-13)
Weeks 3-4: Linked Lists, Stacks, Queues (14-19)
Weeks 5-6: Trees, Graphs (20-32)
Weeks 7-8: Dynamic Programming (33-39)
Weeks 9-10: System Design (40-46)
Weeks 11-12: Behavioral, Mock Interviews (47-60)

Daily Practice

• 2 hours: Solve 2-3 problems from current category
• 30 minutes: Review previous problems
• 30 minutes: Mock system design or behavioral

Common Interview Question Mistakes

1. Practicing Only Easy Problems

Easy problems don’t prepare you for the medium/hard problems in real interviews.

Fix: Spend 70% of time on medium and 20% on hard problems.

2. Solving Without Time Pressure

Taking 45 minutes per problem doesn’t simulate interview conditions.

Fix: Time yourself — 20 min for easy, 35 min for medium, 45 min for hard.

3. Not Reviewing Solutions

Solving a problem once and never reviewing it wastes the learning opportunity.

Fix: Review each problem the next day. Re-solve if you can’t remember the approach.

4. Ignoring Weak Categories

Avoiding DP because it’s hard means DP questions will appear in your interview.

Fix: Practice your weakest category daily until it becomes a strength.

5. Memorizing Solutions Without Understanding

“If the problem has two strings, use DP” is not understanding.

Fix: For each problem, explain why the algorithm works and what would change if constraints changed.

6. Not Practicing Communication

Solving silently doesn’t prepare you for the interview’s interactive format.

Fix: Practice explaining your thinking aloud. Record yourself.

7. Neglecting Behavioral Prep

Assuming technical performance alone gets you the offer. Behavioral rounds can veto a hire.

Fix: Prepare 5-7 stories using the STAR format. Practice telling them naturally.

Practice Questions

1. What is the recommended ratio of easy/medium/hard problems?

20% easy, 60% medium, 20% hard. Or none easy once you can consistently solve mediums.

2. How many questions should you solve before interviewing?

150-200 high-quality problems covering all categories. Quality over quantity — understand each problem deeply.

3. How do you handle a problem you’ve never seen before?

Use the SCORE framework: Situate (understand), Consider (multiple approaches), Outline (plan), Run (code), Evaluate (test).

4. What is the most common interview question category?

Arrays and strings appear in virtually every interview, followed by trees and dynamic programming.

5. How do you track your interview preparation progress?

Track by category: number solved, average difficulty, average time, and questions missed on review.

Challenge: Pick your weakest category from the list above. Solve 10 problems from that category without looking at solutions. Time each problem. After 10, review your average time and accuracy.

FAQ

What’s Next

Built by the developers of Doda Browser, DodaZIP, and Durga Antivirus Pro. Updated 2026-06-20.