This repository is used to storage my solutions for hackerrank challenges.

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Challenges:

• 30 Days of Code
• SQL
• Java
• Interview preparation kit
• Algorithms/Problem Solving
• Regex

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30 Days of Code

• 30 Days of code webpage

Day	Challenge	Solution (Java)	Difficult
0	Day 0: Hello, World.	Solution	Easy
1	Day 1: Data Types	Solution	Easy
2	Day 2: Operators	Solution	Easy
3	Day 3: Intro to Conditional Statements	Solution	Easy
4	Day 4: Class vs. Instance	Solution	Easy
5	Day 5: Loops	Solution	Easy
6	Day 6: Let's Review	Solution	Easy
7	Day 7: Arrays	Solution	Easy
8	Day 8: Dictionaries and Maps	Solution	Easy
9	Day 9: Recursion 3	Solution	Easy
10	Day 10: Binary Numbers	Solution	Easy
11	Day 11: 2D Arrays	Solution	Easy
12	Day 12: Inheritance	Solution	Easy
13	Day 13: Abstract Classes	Solution	Easy
14	Day 14: Scope	Solution	Easy
15	Day 15: Linked List	Solution	Easy
16	Day 16: Exceptions - String to Integer	Solution	Easy
17	Day 17: More Exceptions	Solution	Easy
18	Day 18: Queues and Stacks	Solution	Easy
19	Day 19: Interfaces	Solution	Easy
20	Day 20: Sorting	Solution	Easy
21	Day 21: Generics	Solution	Easy
22	Day 22: Binary Search Trees	Solution	Easy
23	Day 23: BST Level-Order Traversal	Solution	Easy
24	Day 24: More Linked Lists	Solution	Easy
25	Day 25: Running Time and Complexity	Solution	Easy
26	Day 26: Nested Logic	Solution	Easy
27	Day 27: Testing	Solution	Easy
28	Day 28: RegEx, Patterns, and Intro to Databases	Solution	Medium
29	Day 29: Bitwise AND	Solution	Medium

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SQL

• SQL webpage

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

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Java

• Java webpage

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

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Interview preparation kit

• Interview preparation kit webpage

Subdomains	Challenge	Solution	Difficult
Warm-up Challenges	Sales by Match	Solution	Easy
Warm-up Challenges	Couting Vallyes	Solution	Easy
Warm-up Challenges	Jumping on the Clouds	Solution	Easy
Warm-up Challenges	Repeated String	Solution	Easy
Arrays	2D Array - DS	Solution	Easy
Arrays	Arrays: Left Rotation	Solution	Easy
Arrays	New Year Chaos		Medium
Arrays	Minimum Swaps 2	Solution	Medium
Arrays	Array Manipulation		Hard
Dictionaries and Hashmaps	Hash Tables: Ransom Note		Easy
Dictionaries and Hashmaps	Two Strings		Easy
Dictionaries and Hashmaps	Sherlock and Anagrams		Medium
Dictionaries and Hashmaps	Count Triplets		Medium
Dictionaries and Hashmaps	Frequency Queries		Medium
Sorting	Sorting: Bubble Sort		Easy
Sorting	Mark and Toys		Easy
Sorting	Sorting: Comparator		Medium
Sorting	Fraudulent Activity Notifications		Medium
Sorting	Merge Sort: Counting Inversions		Hard
String Manipulation	Strings: Making Anagrams	Solution	Easy
String Manipulation	Alternating Characters	Solution	Easy
String Manipulation	Sherlock and the Valid String		Medium
String Manipulation	Special String Again		Medium
String Manipulation	Common Child		Medium
Greddy Algorithm	Minimum Absolute Difference in an Array		Easy
Greddy Algorithm	Luck Balance		Easy
Greddy Algorithm	Greedy Florist		Medium
Greddy Algorithm	Max Min		Medium
Greddy Algorithm	Reverse Shuffle Merge		Medium

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Problem Solving - Algorithms

• Algorithms webpage

Subdomains	Challenge	Solution	Difficult	Skills
Warmup	Solve Me First	Solution	Easy	Problem Solving (Basic)
Warmup	Simple Array Sum	Solution	Easy	Problem Solving (Basic)
Warmup	Compare the Triplets	Solution	Easy	Problem Solving (Basic)
Warmup	A Very Big Sum	Solution	Easy	Problem Solving (Basic)
Warmup	Diagonal Difference	Solution	Easy	Problem Solving (Basic)
Warmup	Plus Minus	Solution	Easy	Problem Solving (Basic)
Warmup	Staircase	Solution	Easy	Problem Solving (Basic)
Warmup	Mini-Max Sum	Solution	Easy	Problem Solving (Basic)
Warmup	Birthday Cake Candles	Solution	Easy	Problem Solving (Basic)
Warmup	Time Conversion	Solution	Easy	Problem Solving (Basic)
Implementation	Sales by Match	Same from Interview prep. kit	Easy	Problem Solving (Basic)
Implementation	Counting Valleys	Same from Interview prep. kit	Easy	Problem Solving (Basic)
Implementation	Repeated String	Same from Interview prep. kit	Easy	Problem Solving (Basic)
Implementation	Jumping on the Clouds	Same from Interview prep. kit	Easy	Problem Solving (Basic)
Implementation	--	--	--	--

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Regex

• Regex webpage
• Notes

Subdomains	Challenge	Solution	Difficult
Introduction	Matching Specific String	Solution	Easy
Introduction	Matching Anything But a Newline	Solution	Easy
Introduction	Matching Digits & Non-Digit Characters	Solution	Easy
Introduction	Matching Whitespace & Non-Whitespace Character	Solution	Easy
Introduction	Matching Word & Non-Word Character	Solution	Easy
Introduction	Matching Start & End	Solution	Easy
Character Class	Matching Specific Characters	Solution	Easy
Character Class	Excluding Specific Characters	Solution	Easy
Character Class	Matching Character Ranges	Solution	Easy
Repetition	Matching {x} Repetitions	Solution	Easy
Repetition	Matching {x, y} Repetitions	Solution	Easy
Repetition	Matching Zero Or More Repetitions	Solution	Easy
Repetition	Matching One Or More Repetitions	Solution	Easy
Repetition	Matching Ending Items	Solution	Easy
Grouping and Capturing	Matching Word Boundaries	Solution	Easy
Grouping and Capturing	Capturing & Non-Capturing Groups	Solution	Easy
Grouping and Capturing	Alternative Matching	Solution	Easy
Backreferences	Matching Same Text Again & Again	Solution	Easy
Backreferences	Backreferences To Failed Groups	Solution	Easy
Backreferences	Branch Reset Groups	Solution	Easy
Backreferences	Forward References	Solution	Easy
Assertions	Positive Lookahead	Solution	Easy
Assertions	Negative Lookahead	Solution	Easy
Assertions	Positive Lookbehind	Solution	Easy
Assertions	Negative Lookbehind	Solution	Easy
Applications	Detect HTML links		Medium
Applications	Detect HTML Tags		Easy
Applications	Find A Sub-Word		Easy
Applications	Alien Username		Easy
Applications	IP Address Validation		Easy
Applications	Find a Word		Medium
Applications	Detect the Email Addresses		Medium
Applications	Detect the Domain Name		Medium
Applications	Building a Smart IDE: Identifying comments		Medium
Applications	Detecting Valid Latitude and Longitude Pairs		Easy
Applications	HackerRank Tweets		Easy
Applications	Build a Stack Exchange Scraper		Easy
Applications	Utopian Identification Number		Easy
Applications	Valid PAN format		Easy
Applications	Find HackerRank		Easy
Applications	Saying Hi		Easy
Applications	HackerRank Language		Easy
Applications	Building a Smart IDE: Programming Language Detection		Medium
Applications	Split the Phone Numbers		Easy
Applications	Detect HTML Attributes		Easy
Applications	The British and American Style of Spelling		Easy
Applications	UK and US: Part 2		Easy