HackerRank

Solutions to problems on HackerRank

• Java
• Python
• SQL
• Cracking the Coding Interview
• Interview Preparation Kit
• Functional Programming

Java

Subdomain	Challenge	Score	Difficulty	Solution
Introduction	Welcome to Java!	3	Easy	Solution.java
Introduction	Java Stdin and Stdout I	5	Easy	Solution.java
Introduction	Java If-Else	10	Easy	Solution.java
Introduction	Java Stdin and Stdout II	10	Easy	Solution.java
Introduction	Java Output Formatting	10	Easy	Solution.java
Introduction	Java Loops I	10	Easy	Solution.java
Introduction	Java Loops II	10	Easy	Solution.java
Introduction	Java Datatypes	10	Easy	Solution.java
Introduction	Java End-of-file	10	Easy	Solution.java
Introduction	Java Static Initializer Block	10	Easy	Solution.java
Introduction	Java Int to String	10	Easy	Solution.java
Introduction	Java Date and Time	15	Easy	Solution.java
Introduction	Java Currency Formatter	15	Easy	Solution.java
Strings	Java Strings Introduction	5	Easy	Solution.java
Strings	Java Substring	5	Easy	Solution.java
Strings	Java Substring Comparisons	10	Easy	Solution.java
Strings	Java String Reverse	10	Easy	Solution.java
Strings	Java Anagrams	10	Easy	Solution.java
Strings	Java String Tokens	15	Easy	Solution.java
Strings	Pattern Syntax Checker	20	Easy	Solution.java
Strings	Java Regex	25	Medium	Solution.java
Strings	Java Regex 2 - Duplicate Words	25	Medium	Solution.java
Strings	Valid Username Regular Expression	20	Easy	Solution.java
Strings	Tag Content Extractor	20	Medium	Solution.java
BigNumber	Java BigInteger	10	Easy	Solution.java
BigNumber	Java BigDecimal	20	Medium	Solution.java
BigNumber	Java Primality Test	20	Easy	Solution.java
Data Structures	Java 1D Array	5	Easy	Solution.java
Data Structures	Java 2D Array	10	Easy	Solution.java
Data Structures	Java Subarray	10	Easy	Solution.java
Data Structures	Java Arraylist	10	Easy	Solution.java
Data Structures	Java 1D Array (Part 2)	25	Medium	Solution.java
Data Structures	Java List	15	Easy	Solution.java
Data Structures	Java Map	10	Easy	Solution.java
Data Structures	Java Stack	20	Medium	Solution.java
Data Structures	Java Hashset	10	Easy	Solution.java
Data Structures	Java Generics	15	Easy	Solution.java
Data Structures	Java Comparator	10	Medium	Solution.java
Data Structures	Java Sort	10	Easy	Solution.java
Data Structures	Java Dequeue	20	Medium	Solution.java
Data Structures	Java BitSet	20	Easy	Solution.java
Data Structures	Java Priority Queue	20	Medium	Solution.java
Object Oriented Programming	Java Inheritance I	5	Easy	Solution.java
Object Oriented Programming	Java Inheritance II	10	Easy	Solution.java
Object Oriented Programming	Java Abstract Class	10	Easy	Solution.java
Object Oriented Programming	Java Interface	10	Easy	Solution.java
Object Oriented Programming	Java Method Overriding	10	Easy	Solution.java
Object Oriented Programming	Java Method Overriding 2 (Super Keyword)	10	Easy	Solution.java
Object Oriented Programming	Java Instanceof keyword	10	Easy	Solution.java
Object Oriented Programming	Java Iterator	15	Easy	Solution.java
Exception Handling	Java Exception Handling (Try-catch)	10	Easy	Solution.java
Exception Handling	Java Exception Handling	15	Easy	Solution.java
Advanced	Java Varargs - Simple Addition	15	Easy	Solution.java
Advanced	Java Reflection - Attributes	15	Easy	Solution.java
Advanced	Can You Access	15	Medium	Solution.java
Advanced	Prime Checker	25	Medium	Solution.java
Advanced	Java Factory Pattern	15	Easy	Solution.java
Advanced	Java Singleton Pattern	15	Easy	Solution.java
Advanced	Java Visitor Pattern	40	Medium	Solution.java
Advanced	Java Annotations	25	Medium	Solution.java
Advanced	Covariant Return Types	20	Easy	Solution.java
Advanced	Java Lambda Expressions	30	Medium	Solution.java
Advanced	Java MD5	30	Medium	Solution.java
Advanced	Java SHA-256	30	Medium	Solution.java

Python

Subdomain	Challenge	Score	Difficulty	Solution
Introduction	Say "Hello, World!" With Python	5	Easy	Solution.py
Introduction	Python If-Else	10	Easy	Solution.py
Introduction	Arithmetic Operators	10	Easy	Solution.py
Introduction	Python: Division	10	Easy	Solution.py
Introduction	Loops	10	Easy	Solution.py
Introduction	Write a function	10	Medium	Solution.py
Introduction	Print Function	20	Easy	Solution.py
Basic Data Types	List Comprehensions	10	Easy	Solution.py
Basic Data Types	Find the Runner-Up Score!	10	Easy	Solution.py
Basic Data Types	Nested Lists	10	Easy	Solution.py
Basic Data Types	Finding the percentage	10	Easy	Solution.py
Basic Data Types	Lists	10	Easy	Solution.py
Basic Data Types	Tuples	10	Easy	Solution.py
Strings	sWAP cASE	10	Easy	Solution.py
Strings	String Split and Join	10	Easy	Solution.py
Strings	What's Your Name?	10	Easy	Solution.py
Strings	Mutations	10	Easy	Solution.py
Strings	Find a string	10	Easy	Solution.py
Strings	String Validators	10	Easy	Solution.py
Strings	Text Alignment	10	Easy	Solution.py
Strings	Text Wrap	10	Easy	Solution.py
Strings	Designer Door Mat	10	Easy	Solution.py
Strings	String Formatting	10	Easy	Solution.py
Strings	Alphabet Rangoli	20	Easy	Solution.py
Strings	Capitalize!	20	Easy	Solution.py
Strings	The Minion Game	40	Medium	Solution.py
Strings	Merge the Tools!	40	Medium	Solution.py
Sets	Introduction to Sets	10	Easy	Solution.py
Sets	No Idea!	50	Medium	Solution.py
Sets	Symmetric Difference	10	Easy	Solution.py
Sets	Set .add()	10	Easy	Solution.py
Sets	Set .discard(), .remove() & .pop()	10	Easy	Solution.py
Sets	Set .union() Operation	10	Easy	Solution.py
Sets	Set .intersection() Operation	10	Easy	Solution.py
Sets	Set .difference() Operation	10	Easy	Solution.py
Sets	Set .symmetric_difference() Operation	10	Easy	Solution.py
Sets	Set Mutations	10	Easy	Solution.py
Sets	The Captain's Room	10	Easy	Solution.py
Sets	Check Subset	10	Easy	Solution.py
Sets	Check Strict Superset	10	Easy	Solution.py
Math	Polar Coordinates	10	Easy	Solution.py
Math	Find Angle MBC	10	Medium	Solution.py
Math	Triangle Quest 2	20	Medium	Solution.py
Math	Mod Divmod	10	Easy	Solution.py
Math	Power - Mod Power	10	Easy	Solution.py
Math	Integers Come In All Sizes	10	Easy	Solution.py
Math	Triangle Quest	20	Medium	Solution.py
Itertools	itertools.product()	10	Easy	Solution.py
Itertools	itertools.permutations()	10	Easy	Solution.py
Itertools	itertools.combinations()	10	Easy	Solution.py
Itertools	itertools.combinations_with_replacement()	10	Easy	Solution.py
Itertools	Compress the String!	20	Medium	Solution.py
Itertools	Iterables and Iterators	40	Medium	Solution.py
Itertools	Maximize It!	50	Hard	Solution.py
Collections	Collections.Counter()	10	Easy	Solution.py
Collections	DefaultDict Tutorial	20	Easy	Solution.py
Collections	Collections.namedtuple()	20	Easy	Solution.py
Collections	Collections.OrderedDict()	20	Easy	Solution.py
Collections	Word Order	50	Medium	Solution.py
Collections	Collections.deque()	20	Easy	Solution.py
Collections	Company Logo	30	Medium	Solution.py
Collections	Piling Up!	50	Medium	Solution.py
Date and Time	Calendar Module	10	Easy	Solution.py
Date and Time	Time Delta	30	Medium	Solution.py
Errors and Exceptions	Exceptions	10	Easy	Solution.py
Errors and Exceptions	Incorrect Regex	20	Easy	Solution.py
Classes	Classes: Dealing with Complex Numbers	20	Medium	Solution.py
Classes	Class 2 - Find the Torsional Angle	20	Easy	Solution.py
Built-Ins	Zipped!	10	Easy	Solution.py
Built-Ins	Input()	20	Easy	Solution.py
Built-Ins	Python Evaluation	20	Easy	Solution.py
Built-Ins	Athlete Sort	30	Medium	Solution.py
Built-Ins	Any or All	20	Easy	Solution.py
Built-Ins	ginortS	40	Medium	Solution.py
Python Functionals	Map and Lambda Function	20	Easy	Solution.py
Python Functionals	Validating Email Addresses With a Filter	20	Medium	Solution.py
Python Functionals	Reduce Function	30	Medium	Solution.py
Regex and Parsing	Detect Floating Point Number	20	Easy	Solution.py
Regex and Parsing	Re.split()	20	Easy	Solution.py
Regex and Parsing	Group(), Groups() & Groupdict()	20	Easy	Solution.py
Regex and Parsing	Re.findall() & Re.finditer()	20	Easy	Solution.py
Regex and Parsing	Re.start() & Re.end()	20	Easy	Solution.py
Regex and Parsing	Regex Substitution	20	Medium	Solution.py
Regex and Parsing	Validating Roman Numerals	20	Easy	Solution.py
Regex and Parsing	Validating phone numbers	20	Easy	Solution.py
Regex and Parsing	Validating and Parsing Email Addresses	20	Easy	Solution.py
Regex and Parsing	Hex Color Code	30	Easy	Solution.py
Regex and Parsing	HTML Parser - Part 1	30	Easy	Solution.py
Regex and Parsing	HTML Parser - Part 2	30	Easy	Solution.py
Regex and Parsing	Detect HTML Tags, Attributes and Attribute Values	30	Easy	Solution.py
Regex and Parsing	Validating UID	40	Easy	Solution.py
Regex and Parsing	Validating Credit Card Numbers	40	Medium	Solution.py
Regex and Parsing	Validating Postal Codes	80	Hard	Solution.py
Regex and Parsing	Matrix Script	100	Hard	Solution.py
XML	XML 1 - Find the Score	20	Easy	Solution.py
XML	XML2 - Find the Maximum Depth	20	Easy	Solution.py
Closures and Decorators	Standardize Mobile Number Using Decorators	30	Easy	Solution.py
Closures and Decorators	Decorators 2 - Name Directory	30	Easy	Solution.py
Numpy	Arrays	20	Easy	Solution.py
Numpy	Shape and Reshape	20	Easy	Solution.py
Numpy	Transpose and Flatten	20	Easy	Solution.py
Numpy	Concatenate	20	Easy	Solution.py
Numpy	Zeros and Ones	20	Easy	Solution.py
Numpy	Eye and Identity	20	Easy	Solution.py
Numpy	Array Mathematics	20	Easy	Solution.py
Numpy	Floor, Ceil and Rint	20	Easy	Solution.py
Numpy	Sum and Prod	20	Easy	Solution.py
Numpy	Min and Max	20	Easy	Solution.py
Numpy	Mean, Var, and Std	20	Easy	Solution.py
Numpy	Dot and Cross	20	Easy	Solution.py
Numpy	Inner and Outer	20	Easy	Solution.py
Numpy	Polynomials	20	Easy	Solution.py
Numpy	Linear Algebra	20	Easy	Solution.py
Debugging	Words Score	10	Medium	Solution.py
Debugging	Default Arguments	30	Medium	Solution.py

SQL

Subdomain	Challenge	Score	Difficulty	Solution
Basic Select	Revising the Select Query I	10	Easy	Solution.sql
Basic Select	Revising the Select Query II	10	Easy	Solution.sql
Basic Select	Select All	10	Easy	Solution.sql
Basic Select	Select By ID	10	Easy	Solution.sql
Basic Select	Japanese Cities' Attributes	10	Easy	Solution.sql
Basic Select	Japanese Cities' Names	10	Easy	Solution.sql
Basic Select	Weather Observation Station 1	15	Easy	Solution.sql
Basic Select	Weather Observation Station 3	10	Easy	Solution.sql
Basic Select	Weather Observation Station 4	10	Easy	Solution.sql
Basic Select	Weather Observation Station 5	30	Easy	Solution.sql
Basic Select	Weather Observation Station 6	10	Easy	Solution.sql
Basic Select	Weather Observation Station 7	10	Easy	Solution.sql
Basic Select	Weather Observation Station 8	15	Easy	Solution.sql
Basic Select	Weather Observation Station 9	10	Easy	Solution.sql
Basic Select	Weather Observation Station 10	10	Easy	Solution.sql
Basic Select	Weather Observation Station 11	15	Easy	Solution.sql
Basic Select	Weather Observation Station 12	15	Easy	Solution.sql
Basic Select	Higher Than 75 Marks	15	Easy	Solution.sql
Basic Select	Employee Names	10	Easy	Solution.sql
Basic Select	Employee Salaries	10	Easy	Solution.sql
Advanced Select	The PADS	30	Medium	Solution.sql
Advanced Select	Type of Triangle	20	Easy	Solution.sql
Advanced Select	Occupations	30	Medium	Solution.sql
Advanced Select	Binary Tree Nodes	30	Medium	Solution.sql
Advanced Select	New Companies	30	Medium	Solution.sql
Aggregation	Revising Aggregations - The Count Function	10	Easy	Solution.sql
Aggregation	Revising Aggregations - The Sum Function	10	Easy	Solution.sql
Aggregation	Revising Aggregations - Averages	10	Easy	Solution.sql
Aggregation	Average Population	10	Easy	Solution.sql
Aggregation	Japan Population	10	Easy	Solution.sql
Aggregation	Population Density Difference	10	Easy	Solution.sql
Aggregation	The Blunder	15	Easy	Solution.sql
Aggregation	Top Earners	20	Easy	Solution.sql
Aggregation	Weather Observation Station 2	15	Easy	Solution.sql
Aggregation	Weather Observation Station 13	10	Easy	Solution.sql
Aggregation	Weather Observation Station 14	10	Easy	Solution.sql
Aggregation	Weather Observation Station 15	15	Easy	Solution.sql
Aggregation	Weather Observation Station 16	10	Easy	Solution.sql
Aggregation	Weather Observation Station 17	15	Easy	Solution.sql
Aggregation	Weather Observation Station 18	25	Medium	Solution.sql
Aggregation	Weather Observation Station 19	30	Medium	Solution.sql
Aggregation	Weather Observation Station 20	40	Medium	Solution.sql
Basic Join	Asian Population	10	Easy	Solution.sql
Basic Join	African Cities	10	Easy	Solution.sql
Basic Join	Average Population of Each Continent	10	Easy	Solution.sql
Basic Join	The Report	20	Medium	Solution.sql
Basic Join	Top Competitors	30	Medium	Solution.sql
Basic Join	Ollivander's Inventory	30	Medium	Solution.sql
Basic Join	Challenges	30	Medium	Solution.sql
Basic Join	Contest Leaderboard	30	Medium	Solution.sql
Advanced Join	Projects	40	Medium	Solution.sql
Advanced Join	Placements	40	Medium	Solution.sql
Advanced Join	Symmetric Pairs	40	Medium	Solution.sql
Advanced Join	Interviews	50	Hard	Solution.sql
Advanced Join	15 Days of Learning SQL	50	Hard	Solution.sql
Alternative Queries	Draw The Triangle 1	25	Easy	Solution.sql
Alternative Queries	Draw The Triangle 2	25	Easy	Solution.sql
Alternative Queries	Print Prime Numbers	40	Medium	Solution.sql

Cracking the Coding Interview

Subdomain	Challenge	Score	Difficulty	Solution
Data Structures	Arrays: Left Rotation	20	Easy	Solution.java
Data Structures	Strings: Making Anagrams	25	Easy	Solution.java
Data Structures	Hash Tables: Ransom Note	25	Easy	Solution.java
Data Structures	Linked Lists: Detect a Cycle	25	Easy	Solution.java
Data Structures	Stacks: Balanced Brackets	30	Medium	Solution.java
Data Structures	Queues: A Tale of Two Stacks	30	Medium	Solution.java
Data Structures	Trees: Is This a Binary Search Tree?	30	Medium	Solution.java
Data Structures	Heaps: Find the Running Median	50	Hard	Solution.java
Data Structures	Tries: Contacts	50	Hard	Solution.java
Algorithms	Sorting: Bubble Sort	30	Medium	Solution.java
Algorithms	Sorting: Comparator	35	Medium	Solution.java
Algorithms	Merge Sort: Counting Inversions	45	Hard	Solution.java
Algorithms	Hash Tables: Ice Cream Parlor	35	Medium	Solution.java
Algorithms	DFS: Connected Cell in a Grid	45	Hard	Solution.java
Algorithms	BFS: Shortest Reach in a Graph	45	Hard	Solution.java
Techniques / Concepts	Time Complexity: Primality	30	Medium	Solution.java
Techniques / Concepts	Recrusion: Fibonacci Numbers	15	Easy	Solution.java
Techniques / Concepts	Recursion: Davis' Staircase	30	Medium	Solution.java
Techniques / Concepts	DP: Coin Change	60	Hard	Solution.java
Techniques / Concepts	Bit Manipulation: Lonely Integer	20	Easy	Solution.java

Interview Preparation Kit

Subdomain	Challenge	Score	Difficulty	Solution
Warm-up Challenges	Sock Merchant	10	Easy	Solution.java
Warm-up Challenges	Counting Valleys	15	Easy	Solution.java
Warm-up Challenges	Jumping on the Clouds	20	Easy	Solution.java
Warm-up Challenges	Repeated String	20	Easy	Solution.java
Arrays	2D Array - DS	15	Easy	Solution.java
Arrays	Arrays: Left Rotation	20	Easy	Solution.java
Arrays	New Year Chaos	40	Medium	Solution.java
Arrays	Minimum Swaps 2	40	Medium	Solution.java
Arrays	Array Manipulation	60	Hard	Solution.java
Dictionaries and Hashmaps	Hash Tables: Ransom Note	25	Easy	Solution.java
Dictionaries and Hashmaps	Two Strings	25	Easy	Solution.java
Dictionaries and Hashmaps	Sherlock and Anagrams	50	Medium	Solution.java
Sorting	Sorting: Bubble Sort	30	Easy	Solution.java
Sorting	Mark and Toys	35	Easy	Solution.java
Sorting	Sorting: Comparator	35	Medium	Solution.java
Sorting	Merge Sort: Counting Inversions	45	Hard	Solution.java
String Manipulation	Strings: Making Anagrams	25	Easy	Solution.java
String Manipulation	Alternating Characters	20	Easy	Solution.java
Greedy Algorithms	Minimum Absolute Difference in an Array	15	Easy	Solution.java
Greedy Algorithms	Luck Balance	20	Easy	Solution.java
Greedy Algorithms	Greedy Florist	35	Medium	Solution.java
Greedy Algorithms	Max Min	35	Medium	Solution.java
Search	Hash Tables: Ice Cream Parlor	35	Medium	Solution.java
Search	Pairs	50	Medium	Solution.java
Dynamic Programming	Max Array Sum	20	Medium	Solution.java
Dynamic Programming	Candies	50	Medium	Solution.java
Stacks and Queues	Balanced Brackets	25	Medium	Solution.java
Stacks and Queues	Queues: A Tale of Two Stacks	30	Medium	Solution.java
Graphs	BFS: Shortest Reach in a Graph	45	Hard	Solution.java
Graphs	DFS: Connected Cell in a Grid	45	Hard	Solution.java
Trees	Tree: Height of a Binary Tree	10	Easy	Solution.java
Trees	Trees: Is This a Binary Search Tree?	30	Medium	Solution.java
Trees	Binary Search Tree: Lowest Common Ancestor	30	Easy	Solution.java
Linked Lists	Linked Lists: Detect a Cycle	25	Easy	Solution.java
Linked Lists	Reverse a Doubly Linked List	5	Easy	Solution.java
Linked Lists	Find Merge Point of Two Lists	5	Easy	Solution.java
Recursion and Backtracking	Recursion: Fibonacci Numbers	15	Easy	Solution.java
Recursion and Backtracking	Recursion: Davis' Staircase	30	Medium	Solution.java
Miscellaneous	Flipping bits	40	Easy	Solution.java
Miscellaneous	Time Complexity: Primality	30	Medium	Solution.java

Functional Programming

Subdomain	Challenge	Score	Difficulty	Solution
Introduction	Solve Me First FP	3	Easy	Solution.scala
Introduction	Hello World	5	Easy	Solution.scala