HackerRank | Practice, Tutorials & Interview Preparation Solutions
This repository consists of solutions to HackerRank practice, tutorials, and interview preparation problems with Python, mySQL, C#, and JavaScript.
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Table Of Contents
Practices Completed
Python
| Subdomain | Challenge | Problem | Difficulty | Score | Solution |
|---|---|---|---|---|---|
| Introduction | Say 'Hello, World!' With Python | Problem | Easy | 5 | Solution |
| Introduction | Python If-Else | Problem | Easy | 10 | Solution |
| Introduction | Arithmetic Operators | Problem | Easy | 10 | Solution |
| Introduction | Python Division | Problem | Easy | 10 | Solution |
| Introduction | Loops | Problem | Easy | 10 | Solution |
| Introduction | Write a function | Problem | Medium | 10 | Solution |
| Introduction | Print Function | Problem | Easy | 20 | Solution |
| Basic Data Types | List Comprehensions | Problem | Easy | 10 | Solution |
| Basic Data Types | Find the Runner-Up Score! | Problem | Easy | 10 | Solution |
| Basic Data Types | Nested Lists | Problem | Easy | 10 | Solution |
| Basic Data Types | Finding the percentage | Problem | Easy | 10 | Solution |
| Basic Data Types | Lists | Problem | Easy | 10 | Solution |
| Basic Data Types | Tuples | Problem | Easy | 10 | Solution |
| Strings | sWAP cASE | Problem | Easy | 10 | Solution |
| Strings | String Split and Join | Problem | Easy | 10 | Solution |
| Strings | What's Your Name? | Problem | Easy | 10 | Solution |
| Strings | Mutations | Problem | Easy | 10 | Solution |
| Strings | Find a string | Problem | Easy | 10 | Solution |
| Strings | String Validators | Problem | Easy | 10 | Solution |
| Strings | Text Alignment | Problem | Easy | 10 | Solution |
| Strings | Text Wrap | Problem | Easy | 10 | Solution |
| Strings | Designer Door Mat | Problem | Easy | 10 | Solution |
| Strings | String Formatting | Problem | Easy | 10 | Solution |
| Strings | Alphabet Rangoli | Problem | Easy | 20 | Solution |
| Strings | Capitalize! | Problem | Easy | 20 | Solution |
| Strings | The Minion Game | Problem | Medium | 40 | Solution |
| Strings | Merge the Tools! | Problem | Medium | 40 | Solution |
| Sets | Introduction to Sets | Problem | Easy | 10 | Solution |
| Sets | No Idea! | Problem | Medium | 50 | Solution |
| Sets | Symmetric Difference | Problem | Easy | 10 | Solution |
| Sets | Set add() | Problem | Easy | 10 | Solution |
| Sets | Set discard() remove() pop() | Problem | Easy | 10 | Solution |
| Sets | Set union() Operation | Problem | Easy | 10 | Solution |
| Sets | Set intersection() Operation | Problem | Easy | 10 | Solution |
| Sets | Set difference() Operation | Problem | Easy | 10 | Solution |
| Sets | Set symmetric_difference() Operation | Problem | Easy | 10 | Solution |
| Sets | Set Mutations | Problem | Easy | 10 | Solution |
| Sets | The Captain's Room | Problem | Easy | 10 | Solution |
| Sets | Check Subset | Problem | Easy | 10 | Solution |
| Sets | Check Strict Superset | Problem | Easy | 10 | Solution |
| Math | Polar Coordinates | Problem | Easy | 10 | Solution |
| Math | Find Angle MBC | Problem | Medium | 10 | Solution |
| Math | Triangle Quest 2 | Problem | Medium | 20 | Solution |
| Math | Mod Divmod | Problem | Easy | 10 | Solution |
| Math | Power - Mod Power | Problem | Easy | 10 | Solution |
| Math | Integers Come In All Sizes | Problem | Easy | 10 | Solution |
| Math | Triangle Quest | Problem | Medium | 20 | Solution |
| Itertools | itertools.product() | Problem | Easy | 10 | Solution |
| Itertools | itertools.permutations() | Problem | Easy | 10 | Solution |
| Itertools | itertools.combinations() | Problem | Easy | 10 | Solution |
| Itertools | itertools.combinations_with_replacement() | Problem | Easy | 10 | Solution |
| Itertools | Compress the String! | Problem | Medium | 20 | Solution |
| Itertools | Iterables and Iterators | Problem | Medium | 40 | Solution |
| Itertools | Maximize It! | Problem | Hard | 50 | Solution |
| Collections | collections.Counter() | Problem | Easy | 10 | Solution |
| Collections | defaultdict Tutorial | Problem | Easy | 20 | Solution |
| Collections | collections.namedtuple() | Problem | Easy | 20 | Solution |
| Collections | collections.OrderedDict() | Problem | Easy | 20 | Solution |
| Collections | collections.deque() | Problem | Easy | 20 | Solution |
| Collections | Company Logo | Problem | Medium | 40 | Solution |
| Collections | Word Order | Problem | Medium | 50 | Solution |
| Collections | Piling Up! | Problem | Medium | 50 | Solution |
| Date and Time | Calendar Module | Problem | Easy | 10 | Solution |
| Date and Time | Time Delta | Problem | Medium | 30 | Solution |
| Errors and Exceptions | Exceptions | Problem | Easy | 10 | Solution |
| Errors and Exceptions | Incorrect Regex | Problem | Easy | 20 | Solution |
| Classes | Classes - Dealing with Complex Numbers | Problem | Medium | 20 | Solution |
| Classes | Class 2 - Find the Torsional Angle | Problem | Easy | 20 | Solution |
Regex
| Subdomain | Challenge | Problem | Difficulty | Score | Solution |
|---|---|---|---|---|---|
| Introduction | Matching Specific String | Problem | Easy | 5 | Solution |
| Introduction | Matching Anything But a Newline | Problem | Easy | 5 | Solution |
| Introduction | Matching Digits & Non-Digit Characters | Problem | Easy | 5 | Solution |
| Introduction | Matching Whitespace & Non-Whitespace Character | Problem | Easy | 5 | Solution |
| Introduction | Matching Word & Non-Word Character | Problem | Easy | 5 | Solution |
| Introduction | Matching Start & End | Problem | Easy | 5 | Solution |
| Character Class | Matching Specific Characters | Problem | Easy | 10 | Solution |
| Character Class | Excluding Specific Characters | Problem | Easy | 10 | Solution |
| Character Class | Matching Character Ranges | Problem | Easy | 10 | Solution |
| Repetitions | Matching {x} Repetitions | Problem | Easy | 20 | Solution |
| Repetitions | Matching {x, y} Repetitions | Problem | Easy | 20 | Solution |
| Repetitions | Matching Zero Or More Repetitions | Problem | Easy | 20 | Solution |
| Repetitions | Matching One Or More Repetitions | Problem | Easy | 20 | Solution |
| Repetitions | Matching Ending Items | Problem | Easy | 20 | Solution |
| Grouping and Capturing | Matching Word Boundaries | Problem | Easy | 20 | Solution |
| Grouping and Capturing | Capturing & Non-Capturing Groups | Problem | Easy | 20 | Solution |
| Grouping and Capturing | Alternative Matching | Problem | Easy | 20 | Solution |
| Backreferences | Matching Same Text Again & Again | Problem | Easy | 20 | Solution |
| Backreferences | Backreferences To Failed Groups | Problem | Easy | 20 | Solution |
| Backreferences | Branch Reset Groups | Problem | Easy | 20 | Solution |
| Backreferences | Forward References | Problem | Easy | 20 | Solution |
| Assertions | Positive Lookahead | Problem | Easy | 20 | Solution |
| Assertions | Negative Lookahead | Problem | Easy | 20 | Solution |
| Assertions | Positive Lookbehind | Problem | Easy | 20 | Solution |
| Assertions | Negative Lookbehind | Problem | Easy | 20 | Solution |
Security
| Subdomain | Challenge | Problem | Difficulty | Score | Solution |
|---|---|---|---|---|---|
| Functions | Security Functions | Problem | Easy | 5 | Solution |
| Functions | Security Functions II | Problem | Easy | 5 | Solution |
| Functions | Security Bijective Functions | Problem | Easy | 10 | Solution |
| Functions | Security Function Inverses | Problem | Easy | 10 | Solution |
| Functions | Security Permutations | Problem | Easy | 10 | Solution |
| Functions | Security Involution | Problem | Easy | 10 | Solution |
| Terminology and Concepts | Security - Message Space and Ciphertext Space | Problem | Easy | 10 | Solution |
| Terminology and Concepts | Security Key Spaces | Problem | Easy | 10 | Solution |
| Terminology and Concepts | Security Encryption Scheme | Problem | Easy | 10 | Solution |
| Cryptography | PRNG Sequence Guessing | Problem | Medium | 50 | Solution |
| Cryptography | Keyword Transposition Cipher | Problem | Easy | 50 | Solution |
| Cryptography | Basic Cryptanalysis | Problem | Hard | 50 | Solution |
SQL
| Subdomain | Challenge | Problem | Difficulty | Score | Solution |
|---|---|---|---|---|---|
| Basic Select | Reversing the Select Query I | Problem | Easy | 10 | Solution |
| Basic Select | Revising the Select Query II | Problem | Easy | 10 | Solution |
| Basic Select | Select All | Problem | Easy | 10 | Solution |
| Basic Select | Select By ID | Problem | Easy | 10 | Solution |
| Basic Select | Japanese Cities' Attributes | Problem | Easy | 10 | Solution |
| Basic Select | Japanese Cities' Names | Problem | Easy | 10 | Solution |
| Basic Select | Weather Observation Station 1 | Problem | Easy | 15 | Solution |
| Basic Select | Weather Observation Station 3 | Problem | Easy | 10 | Solution |
| Basic Select | Weather Observation Station 4 | Problem | Easy | 10 | Solution |
| Basic Select | Weather Observation Station 5 | Problem | Easy | 30 | Solution |
| Basic Select | Weather Observation Station 6 | Problem | Easy | 10 | Solution |
| Basic Select | Weather Observation Station 7 | Problem | Easy | 10 | Solution |
| Basic Select | Weather Observation Station 8 | Problem | Easy | 15 | Solution |
| Basic Select | Weather Observation Station 9 | Problem | Easy | 10 | Solution |
| Basic Select | Weather Observation Station 10 | Problem | Easy | 10 | Solution |
| Basic Select | Weather Observation Station 11 | Problem | Easy | 15 | Solution |
| Basic Select | Weather Observation Station 12 | Problem | Easy | 15 | Solution |
| Basic Select | Higher Than 75 Marks | Problem | Easy | 15 | Solution |
| Basic Select | Employee Names | Problem | Easy | 10 | Solution |
| Basic Select | Employee Salaries | Problem | Easy | 10 | Solution |
| Advanced Select | Type of Triangle | Problem | Easy | 20 | Solution |
| Advanced Select | The PADS | Problem | Medium | 30 | Solution |
| Advanced Select | Occupations | Problem | Medium | 30 | Solution |
| Advanced Select | Binary Tree Nodes | Problem | Medium | 30 | Solution |
| Advanced Select | New Companies | Problem | Medium | 30 | Solution |
| Aggregation | Revising Aggregations - The Count Function | Problem | Easy | 10 | Solution |
| Aggregation | Revising Aggregations - The Sum Function | Problem | Easy | 10 | Solution |
| Aggregation | Revising Aggregations - Averages | Problem | Easy | 10 | Solution |
| Aggregation | Average Population | Problem | Easy | 10 | Solution |
| Aggregation | Japan Population | Problem | Easy | 10 | Solution |
| Aggregation | Population Density Difference | Problem | Easy | 10 | Solution |
| Aggregation | The Blunder | Problem | Easy | 15 | Solution |
| Aggregation | Top Earners | Problem | Easy | 20 | Solution |
| Aggregation | Weather Observation Station 2 | Problem | Easy | 15 | Solution |
| Aggregation | Weather Observation Station 13 | Problem | Easy | 10 | Solution |
| Aggregation | Weather Observation Station 14 | Problem | Easy | 10 | Solution |
| Aggregation | Weather Observation Station 15 | Problem | Easy | 15 | Solution |
| Aggregation | Weather Observation Station 16 | Problem | Easy | 10 | Solution |
| Aggregation | Weather Observation Station 17 | Problem | Easy | 15 | Solution |
| Aggregation | Weather Observation Station 18 | Problem | Medium | 25 | Solution |
| Aggregation | Weather Observation Station 19 | Problem | Medium | 30 | Solution |
| Aggregation | Weather Observation Station 20 | Problem | Medium | 40 | Solution |
Tutorials Completed
10 Days of JavaScript
| Day | Challenge | Problem | Difficulty | Score | Solution |
|---|---|---|---|---|---|
| 0 | Hello, World! | Problem | Easy | 10 | Solution |
| 0 | Data Types | Problem | Easy | 10 | Solution |
| 1 | Arithmetic Operators | Problem | Easy | 10 | Solution |
| 1 | Functions | Problem | Easy | 10 | Solution |
| 1 | Let and Const | Problem | Easy | 10 | Solution |
| 2 | Conditional Statements - If-Else | Problem | Easy | 10 | Solution |
| 2 | Conditional Statements - Switch | Problem | Easy | 10 | Solution |
| 2 | Loops | Problem | Easy | 10 | Solution |
| 3 | Arrays | Problem | Easy | 15 | Solution |
| 3 | Try, Catch, and Finally | Problem | Easy | 15 | Solution |
| 3 | Throw | Problem | Easy | 15 | Solution |
| 4 | Create a Rectangle Object | Problem | Easy | 15 | Solution |
| 4 | Count Objects | Problem | Easy | 15 | Solution |
| 4 | Classes | Problem | Easy | 15 | Solution |
| 5 | Inheritance | Problem | Easy | 15 | Solution |
| 5 | Template Literals | Problem | Easy | 15 | Solution |
| 5 | Arrow Functions | Problem | Easy | 15 | Solution |
| 6 | Bitwise Operators | Problem | Easy | 15 | Solution |
| 6 | JavaScript Dates | Problem | Easy | 15 | Solution |
| 7 | Regular Expressions I | Problem | Easy | 15 | Solution |
| 7 | Regular Expressions II | Problem | Easy | 15 | Solution |
| 7 | Regular Expressions III | Problem | Easy | 15 | Solution |
| 8 | Create a Button | Problem | Easy | 20 | Solution |
| 8 | Buttons Container | Problem | Easy | 25 | Solution |
| 9 | Binary Calculator | Problem | Medium | 30 | Solution |
10 Days of Statistics
| Day | Challenge | Problem | Difficulty | Score | Solution |
|---|---|---|---|---|---|
| 0 | Mean, Median, and Mode | Problem | Easy | 30 | Solution |
| 0 | Weighted Mean | Problem | Easy | 30 | Solution |
| 1 | Quartiles | Problem | Easy | 30 | Solution |
| 1 | Interquartile Range | Problem | Easy | 30 | Solution |
| 1 | Standard Deviation | Problem | Easy | 30 | Solution |
| 2 | Basic Probability | Problem | Easy | 10 | Solution |
| 2 | More Dice | Problem | Easy | 10 | Solution |
| 2 | Compound Event Probability | Problem | Easy | 10 | Solution |
| 3 | Conditional Probability | Problem | Easy | 10 | Solution |
| 3 | Cards of the Same Suit | Problem | Easy | 10 | Solution |
| 3 | Drawing Marbles | Problem | Easy | 10 | Solution |
| 4 | Binomial Distribution I | Problem | Easy | 30 | Solution |
| 4 | Binomial Distribution II | Problem | Easy | 30 | Solution |
| 4 | Geometric Distribution I | Problem | Easy | 30 | Solution |
| 4 | Geometric Distribution II | Problem | Easy | 30 | Solution |
| 5 | Poisson Distribution I | Problem | Easy | 30 | Solution |
| 5 | Poisson Distribution II | Problem | Easy | 30 | Solution |
| 5 | Normal Distribution I | Problem | Easy | 30 | Solution |
| 5 | Normal Distribution II | Problem | Easy | 30 | Solution |
| 6 | The Central Limit Theorem I | Problem | Easy | 30 | Solution |
| 6 | The Central Limit Theorem II | Problem | Easy | 30 | Solution |
| 6 | The Central Limit Theorem III | Problem | Easy | 30 | Solution |
| 7 | Pearson Correlation Coefficient I | Problem | Easy | 30 | Solution |
| 7 | Spearman's Rank Correlation Coefficient | Problem | Easy | 30 | Solution |
| 8 | Least Square Regression Line | Problem | Easy | 30 | Solution |
| 8 | Pearson Correlation Coefficient II | Problem | Easy | 30 | Solution |
| 9 | Multiple Linear Regression | Problem | Medium | 30 | Solution |
30 Days of Code
| Day | Challenge | Problem | Difficulty | Score | Python | C# |
|---|---|---|---|---|---|---|
| 0 | Hello, World | Problem | Easy | 30 | Solution | Solution |
| 1 | Data Types | Problem | Easy | 30 | Solution | Solution |
| 2 | Operators | Problem | Easy | 30 | Solution | Solution |
| 3 | Intro to Conditional Statements | Problem | Easy | 30 | Solution | Solution |
| 4 | Class vs. Instance | Problem | Easy | 30 | Solution | Solution |
| 5 | Loops | Problem | Easy | 30 | Solution | Solution |
| 6 | Let's Review | Problem | Easy | 30 | Solution | Solution |
| 7 | Arrays | Problem | Easy | 30 | Solution | Solution |
| 8 | Dictionaries and Maps | Problem | Easy | 30 | Solution | Solution |
| 9 | Recursion 3 | Problem | Easy | 30 | Solution | Solution |
| 10 | Binary Numbers | Problem | Easy | 30 | Solution | Solution |
| 11 | 2D Arrays | Problem | Easy | 30 | Solution | Solution |
| 12 | Inheritance | Problem | Easy | 30 | Solution | Solution |
| 13 | Abstract Classes | Problem | Easy | 30 | Solution | Solution |
| 14 | Scope | Problem | Easy | 30 | Solution | Solution |
| 15 | Linked List | Problem | Easy | 30 | Solution | Solution |
| 16 | Exceptions - String to Integer | Problem | Easy | 30 | Solution | Solution |
| 17 | More Exceptions | Problem | Easy | 30 | Solution | Solution |
| 18 | Queues and Stack | Problem | Easy | 30 | Solution | Solution |
| 19 | Interfaces | Problem | Easy | 30 | Solution | Solution |
| 20 | Sorting | Problem | Easy | 30 | Solution | Solution |
| 21 | Generics | Problem | Easy | 30 | Solution | Solution |
| 22 | Binary Search Trees | Problem | Easy | 30 | Solution | Solution |
| 23 | BST Level-Order Traversal | Problem | Easy | 30 | Solution | Solution |
| 24 | More Linked Lists | Problem | Easy | 30 | Solution | Solution |
| 25 | Running Time and Complexity | Problem | Medium | 30 | Solution | Solution |
| 26 | Nested Logic | Problem | Easy | 30 | Solution | Solution |
| 27 | Testing | Problem | Easy | 30 | Solution | Solution |
| 28 | RegEx, Patterns, and Intro to Databases | Problem | Medium | 30 | Solution | Solution |
| 29 | Bitwise AND | Problem | Medium | 30 | Solution | Solution |
Interview Preparation Kit
| Domain | Challenge | Problem | Difficulty | Score | Solution |
|---|---|---|---|---|---|
| Warm-up Challenges | Sock Merchant | Problem | Easy | 10 | Solution |
| Warm-up Challenges | Counting Valleys | Problem | Easy | 15 | Solution |
| Warm-up Challenges | Jumping on the Clouds | Problem | Easy | 20 | Solution |
| Warm-up Challenges | Repeated String | Problem | Easy | 20 | Solution |
| Arrays | 2D Arrays - DS | Problem | Easy | 15 | Solution |
| Arrays | Arrays - Left Rotation | Problem | Easy | 20 | Solution |
| Arrays | New Year Chaos | Problem | Medium | 40 | Solution |
| Arrays | Minimum Swaps 2 | Problem | Medium | 40 | Solution |
| Arrays | Array Manipulation | Problem | Hard | 60 | Solution |
| Dictionaries and Hashmaps | Hash Tables - Ransom Note | Problem | Easy | 25 | Solution |
| Dictionaries and Hashmaps | Two Strings | Problem | Easy | 25 | Solution |
| Dictionaries and Hashmaps | Sherlock and Anagrams | Problem | Medium | 50 | Solution |
| Dictionaries and Hashmaps | Count Triplets | Problem | Medium | 35 | Solution |
| Dictionaries and Hashmaps | Frequency Queries | Problem | Medium | 40 | Solution |
| Sorting | Sorting - Bubble Sort | Problem | Easy | 30 | Solution |
| Sorting | Mark and Toys | Problem | Easy | 35 | Solution |
| Sorting | Sorting - Comparator | Problem | Medium | 35 | Solution |
| Sorting | Fraudulent Activity Notifications | Problem | Medium | 40 | Solution |
| Sorting | Merge Sort - Counting Inversions | Problem | Hard | 45 | Solution |
| String Manipulation | Strings - Making Anagrams | Problem | Easy | 25 | Solution |
| String Manipulation | Alternating Characters | Problem | Easy | 20 | Solution |
| String Manipulation | Sherlock and the Valid String | Problem | Medium | 35 | Solution |
| String Manipulation | Special String Again | Problem | Medium | 40 | Solution |
| String Manipulation | Common Child | Problem | Hard | 60 | Solution |
| Greedy Algorithm | Minimum Absolute Difference in an Array | Problem | Easy | 15 | Solution |
| Greedy Algorithm | Luck Balance | Problem | Easy | 20 | Solution |
| Greedy Algorithm | Greedy Florist | Problem | Medium | 35 | Solution |
| Greedy Algorithm | Max Min | Problem | Medium | 35 | Solution |
| Greedy Algorithm | Reverse Shuffle Merge | Problem | Advanced | 50 | Solution |
Certificates
| Skill | Test | Difficulty | Description | Certificate |
|---|---|---|---|---|
| Angular | Test | Basic | MVC Frameworks, Components (Angular, Dynamic, Styling), TypeScript, Two Way Binding and Form Validation | Certificate |
| Angular | Test | Intermediate | Routing, NgModules, Observables for data transmission and event handling, Dependency Injections, and APIs | Certificate |
| C# | Test | Basic | Data Types, and Variables, OOP, Properties and Indexers, Collections, Exception handling, among others | Certificate |
| CSS | Test | Basic | Text Styling Fundamentals, Layouts, Boxing of Elements, among others | Certificate |
| Python | Test | Basic | Scalar Types, Operators and Control Flow, Strings, Collections and Iteration, Modularity, Objects and Types and Classes | Certificate |
| Java | Test | Basic | Classes, Data Structures, Inheritance, Exception Handling, among others | Certificate |
| JavaScript | Test | Basic | Functions, Currying, Hoisting, Scope, Inheritance, Events and Error Handling | Certificate |
| JavaScript | Test | Intermediate | Design Patterns, Memory Management, Concurrency Model, and Event Loops, among others | Certificate |
| Node | Test | Basic | Package and Modules Management, Callbacks, Event Loop, Event Emitter, Buffers, Streams and File Systems | Certificate |
| React | Test | Basic | Basic Routing, Rendering Elements, State Management (Internal Component State), Handling Events, ES6 and JavaScript and Form Validation | Certificate |
| Problem Solving | Test | Basic | Data Structures (such as Arrays, Strings) and Algorithms (such as Sorting and Searching) | Certificate |
| REST API | Test | Intermediate | Retrieving data from an API and process using parameters or paging | Certificate |
| SQL | Test | Basic | Queries, Relationships, and Aggregators | Certificate |
| SQL | Test | Intermediate | Complex joins, Unions, and Sub-Queries | Certificate |
| SQL | Test | Advanced | Query Optimization, Data Modelling, Indexing, Window Functions, and Pivots | Certificate |
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