320 efficient solutions to HackerRank problems

• 10 Days of Statistics
• 30 Days of Code
• Algorithms
• Cracking the Coding Interview
• Data Structures
• General Programming
• Implementation
• Java
• SQL

Solutions are coded using Java 8

SQL solutions are coded using MySQL

10 Days of Statistics

Day	Challenge	Points	Solution
0	Mean, Median, and Mode	30	Solution.java
0	Weighted Mean	30	Solution.java
1	Quartiles	30	Solution.java
1	Interquartile Range	30	Solution.java
1	Standard Deviation	30	Solution.java
2	Basic Probability	10	Solution
2	More Dice	10	Solution
2	Compound Event Probability	10	Solution
3	Conditional Probability	10	Solution
3	Cards of the Same Suit	10	Solution
3	Drawing Marbles	10	Solution
4	Binomial Distribution I	30	Solution.java
4	Binomial Distribution II	30	Solution.java
4	Geometric Distribution I	30	Solution.java
4	Geometric Distribution II	30	Solution.java
5	Poisson Distribution I	30	Solution.java
5	Poisson Distribution II	30	Solution.java
5	Normal Distribution I	30	Solution.java
5	Normal Distribution II	30	Solution.java
6	The Central Limit Theorem I	30	Solution.java
6	The Central Limit Theorem II	30	Solution.java
6	The Central Limit Theorem III	30	Solution.java
7	Pearson Correlation Coefficient I	30	Solution.java
7	Spearman's Rank Correlation Coefficient	30	Solution.java
8	Least Square Regression Line	30	Solution.java
8	Pearson Correlation Coefficient II	30	Solution
9	Multiple Linear Regression	30	Solution.java

30 Days of Code

Day	Challenge	Points	Solution
0	Hello, World	30	Solution.java
1	Data Types	30	Solution.java
2	Operators	30	Solution.java
3	Intro to Conditional Statements	30	Solution.java
4	Class vs. Instance	30	Solution.java
5	Loops	30	Solution.java
6	Let's Review	30	Solution.java
7	Arrays	30	Solution.java
8	Dictionaries and Maps	30	Solution.java
9	Recursion	30	Solution.java
10	Binary Numbers	30	Solution.java
11	2D Arrays	30	Solution.java
12	Inheritance	30	Solution.java
13	Abstract Classes	30	Solution.java
14	Scope	30	Solution.java
15	Linked List	30	Solution.java
16	Exceptions - String to Integer	30	Solution.java
17	More Exceptions	30	Solution.java
18	Queues and Stacks	30	Solution.java
19	Interfaces	30	Solution.java
20	Sorting	30	Solution.java
21	Generics	30	Solution.java
22	Binary Search Trees	30	Solution.java
23	BST Level-Order Traversal	30	Solution.java
24	More Linked Lists	30	Solution.java
25	Running Time and Complexity	30	Solution.java
26	Nested Logic	30	Solution.java
27	Testing	30	Solution.java

Algorithms

Subdomain	Challenge	Points	Solution
Sorting	Quicksort 1 - Partition	10	Solution.java
Sorting	Marc's Cakewalk	15	Solution.java
Sorting	Minimum Absolute Difference in an Array	15	Solution.java
Sorting	Luck Balance	20	Solution.java
Sorting	Insertion Sort - Part 1	30	Solution.java
Sorting	Insertion Sort - Part 2	30	Solution.java
Sorting	Correctness and the Loop Invariant	30	Solution.java
Sorting	Running Time of Algorithms	30	Solution.java
Sorting	Quicksort 2 - Sorting	30	Solution.java
Sorting	Counting Sort 1	30	Solution.java
Sorting	Counting Sort 2	30	Solution.java
Sorting	Counting Sort 3	30	Solution.java
Sorting	Intro to Tutorial Challenges	30	Solution.java
Sorting	Quicksort In-Place	35	Solution.java
Sorting	Running Time of Quicksort	35	Solution.java
Sorting	The Full Counting Sort	40	Solution.java
Search	Ice Cream Parlor	30	Solution.java
Search	Connected Cells in a Grid	50	Solution.java
Greedy	Grid Challenge	20	Solution.java
Greedy	Maximum Perimeter Triangle	20	Solution.java
Greedy	Beautiful Pairs	30	Solution.java
Graph Theory	Breadth First Search - Shortest Reach	55	Solution.java
Strings	Super Reduced String	10	Solution.java
Strings	CamelCase	15	Solution.java
Strings	Two Characters	15	Solution.java
Strings	Caesar Cipher	15	Solution.java
Strings	Mars Exploration	15	Solution.java
Strings	Weighted Uniform Strings	20	Solution.java
Strings	Gemstones	20	Solution.java
Strings	Alternating Characters	20	Solution.java
Strings	Beautiful Binary String	20	Solution.java
Strings	The Love-Letter Mystery	20	Solution.java
Strings	String Construction	25	Solution.java
Dynamic Programming	The Coin Change Problem	60	Solution.java
Bit Manipulation	Lonely Integer	20	Solution.java
Bit Manipulation	Bit Manipulation: Lonely Integer	20	Solution.java
Bit Manipulation	Sum vs XOR	25	Solution.java
Bit Manipulation	Maximizing XOR	30	Solution.java
Bit Manipulation	Sansa and XOR	30	Solution.java
Bit Manipulation	Counter game	30	Solution.java

Cracking the Coding Interview

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

Data Structures

Subdomain	Challenge	Points	Solution
Arrays	Arrays - DS	10	Solution.java
Arrays	2D Array - DS	15	Solution.java
Arrays	Dynamic Array	15	Solution.java
Arrays	Left Rotation	20	Solution.java
Arrays	Sparse Arrays	25	Solution.java
Arrays	Algorithmic Crush	60	Solution.java
Stacks	Maximum Element	20	Solution.java
Stacks	Balanced Brackets	25	Solution.java
Trees	Tree: Preorder Traversal	10	Solution.java
Trees	Tree: Inorder Traversal	10	Solution.java
Trees	Tree: Postorder Traversal	10	Solution.java
Trees	Tree: Height of a Binary Tree	10	Solution.java
Trees	Tree: Level Order Traversal	20	Solution.java
Trees	Tree: Huffman Decoding	20	Solution.java
Trees	Tree: Top View	20	Solution.java
Trees	Binary Search Tree: Insertion	20	Solution.java
Trees	Binary Search Tree: Lowest Common Ancestor	30	Solution.java
Trees	Is This a Binary Search Tree?	30	Solution.java
Trees	Swap Nodes [Algo]	40	Solution.java
Trees	Square-Ten Tree	60	Solution.java
Linked List	Print the Elements of a Linked List	5	Solution.java
Linked List	Insert a node at the head of a linked list	5	Solution.java
Linked List	Insert a Node at the Tail of a Linked List	5	Solution.java
Linked List	Insert a node at a specific position in a linked list	5	Solution.java
Linked List	Delete a Node	5	Solution.java
Linked List	Print in Reverse	5	Solution.java
Linked List	Reverse a linked list	5	Solution.java
Linked List	Compare two linked lists	5	Solution.java
Linked List	Merge two sorted linked lists	5	Solution.java
Linked List	Get Node Value	5	Solution.java
Linked List	Delete duplicate-value nodes from a sorted linked list	5	Solution.java
Linked List	Cycle Detection	5	Solution.java
Linked List	Find Merge Point of Two Lists	5	Solution.java
Linked List	Inserting a Node Into a Sorted Doubly Linked List	5	Solution.java
Linked List	Reverse a doubly linked list	5	Solution.java
Tries	Contacts	40	Solution.java
Queues	Queue using Two Stacks	30	Solution.java
Heaps	Find the Running Median	50	Solution.java
Multiple Choice	Data Structures MCQ 1	5	Solution
Multiple Choice	Data Structures MCQ 2	5	Solution
Multiple Choice	Data Structures MCQ 3	5	Solution

General Programming

Subdomain	Challenge	Points	Solution
Basic Programming	Solve Me First	1	Solution.java
Basic Programming	Staircase	10	Solution.java
Basic Programming	Plus Minus	10	Solution.java
Basic Programming	Diagonal Difference	10	Solution.java
Basic Programming	A Very Big Sum	10	Solution.java
Basic Programming	Simple Array Sum	10	Solution.java
Basic Programming	Compare the Triplets	10	Solution.java
Basic Programming	Divisible Sum Pairs	10	Solution.java
Basic Programming	Kangaroo	10	Solution.java
Basic Programming	Drawing Book	10	Solution.java
Basic Programming	Birthday Cake Candles	10	Solution.java
Basic Programming	Bon Appetit	10	Solution.java
Basic Programming	Sock Merchant	10	Solution.java
Basic Programming	Apple and Orange	10	Solution.java
Basic Programming	Between Two Sets	10	Solution.java
Basic Programming	Mini-max Sum	10	Solution.java
Basic Programming	Grading Students	10	Solution.java
Basic Programming	Breaking the Records	10	Solution.java
Basic Programming	Migratory Birds	10	Solution.java
Basic Programming	Birthday Chocolate	10	Solution.java
Basic Programming	Time Conversion	15	Solution.java
Basic Programming	Library Fine	15	Solution.java
Basic Programming	Save the Prisoner!	15	Solution.java
Basic Programming	Jumping on the Clouds - Revisited	15	Solution.java
Basic Programming	Counting Valleys	15	Solution.java
Basic Programming	Viral Advertising	15	Solution.java
Basic Programming	Beautiful Days at the Movies	15	Solution.java
Basic Programming	Electronics Shop	15	Solution.java
Basic Programming	Cats and a Mouse	15	Solution.java
Basic Programming	The Hurdle Race	15	Solution.java
Basic Programming	Utopian Tree	20	Solution.java
Basic Programming	Circular Array Rotation	20	Solution.java
Basic Programming	Sherlock and Squares	20	Solution.java
Basic Programming	Angry Professor	20	Solution.java
Basic Programming	Extra Long Factorials	20	Solution.java
Basic Programming	Minimum Distances	20	Solution.java
Basic Programming	Beautiful Triplets	20	Solution.java
Basic Programming	Jumping on the Clouds	20	Solution.java
Basic Programming	Equalize the Array	20	Solution.java
Basic Programming	Designer PDF Viewer	20	Solution.java
Basic Programming	Repeated String	20	Solution.java
Basic Programming	Append and Delete	20	Solution.java
Basic Programming	Picking Numbers	20	Solution.java
Basic Programming	Climbing the Leaderboard	20	Solution.java
Basic Programming	Sequence Equation	20	Solution.java
Basic Programming	Find Digits	25	Solution.java
Basic Programming	Cut the sticks	25	Solution.java
Basic Programming	Taum and B'day	25	Solution.java
Basic Programming	Flatland Space Stations	25	Solution.java
Basic Programming	Fair Rations	25	Solution.java
Basic Programming	Manasa and Stones	30	Solution.java
Object-Oriented Programming	Class vs. Instance	30	Solution.java
Object-Oriented Programming	Inheritance	30	Solution.java
Object-Oriented Programming	Abstract Classes	30	Solution.java
RegEx	HackerRank in a String!	20	Solution.java

Implementation

Subdomain	Challenge	Difficulty	Solution
Brute Force	Pangrams	20	Solution.java
Brute Force	Strings: Making Anagrams	25	Solution.java
Brute Force	Making Anagrams	30	Solution.java
Brute Force	Modified Kaprekar Numbers	30	Solution.java

Java

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

SQL

Subdomain	Challenge	Points	Solution
Basic Select	Revising the Select Query I	10	MySQL Solution
Basic Select	Revising the Select Query II	10	MySQL Solution
Basic Select	Select All	10	MySQL Solution
Basic Select	Select By ID	10	MySQL Solution
Basic Select	Japanese Cities' Attributes	10	MySQL Solution
Basic Select	Japanese Cities' Names	10	MySQL Solution
Basic Select	Weather Observation Station 1	15	MySQL Solution
Basic Select	Weather Observation Station 3	10	MySQL Solution
Basic Select	Weather Observation Station 4	10	MySQL Solution
Basic Select	Weather Observation Station 5	30	MySQL Solution
Basic Select	Weather Observation Station 6	10	MySQL Solution
Basic Select	Weather Observation Station 7	10	MySQL Solution
Basic Select	Weather Observation Station 8	15	MySQL Solution
Basic Select	Weather Observation Station 9	10	MySQL Solution
Basic Select	Weather Observation Station 10	10	MySQL Solution
Basic Select	Weather Observation Station 11	15	MySQL Solution
Basic Select	Weather Observation Station 12	15	MySQL Solution
Basic Select	Higher Than 75 Marks	15	MySQL Solution
Basic Select	Employee Names	10	MySQL Solution
Basic Select	Employee Salaries	10	MySQL Solution
Basic Join	Asian Population	10	MySQL Solution
Basic Join	African Cities	10	MySQL Solution
Basic Join	Average Population of Each Continent	10	MySQL Solution
Basic Join	The Report	20	MySQL Solution
Aggregation	Revising Aggregations - The Count Function	10	MySQL Solution
Aggregation	Revising Aggregations - The Sum Function	10	MySQL Solution
Aggregation	Revising Aggregations - Averages	10	MySQL Solution
Aggregation	Average Population	10	MySQL Solution
Aggregation	Japan Population	10	MySQL Solution
Aggregation	Population Density Difference	10	MySQL Solution
Aggregation	The Blunder	15	MySQL Solution
Aggregation	Top Earners	20	MySQL Solution
Aggregation	Weather Observation Station 2	15	MySQL Solution
Aggregation	Weather Observation Station 13	10	MySQL Solution
Aggregation	Weather Observation Station 14	10	MySQL Solution
Aggregation	Weather Observation Station 15	15	MySQL Solution
Aggregation	Weather Observation Station 16	10	MySQL Solution
Aggregation	Weather Observation Station 17	15	MySQL Solution
Aggregation	Weather Observation Station 18	25	MySQL Solution
Aggregation	Weather Observation Station 19	30	MySQL Solution