30 Days of Code

Day	Challenge	Difficulty	Points	Solution
0	Hello, World	Easy	30
1	Data Types	Easy	30
2	Operators	Easy	30
3	Intro to Conditional Statements	Easy	30
4	Class vs. Instance	Easy	30
5	Loops	Easy	30
6	Let's Review	Easy	30

Interview Preparation Kit

Subdomain	Challenge	Difficulty	Points	Solution
Warm-up Challenges	Sock Merchant	Easy	10
Warm-up Challenges	Counting Valleys	Easy	15
Warm-up Challenges	Jumping on the Clouds	Easy	20
Warm-up Challenges	Repeated String	Easy	20
Arrays	2D Array - DS	Easy	15
Arrays	Arrays: Left Rotation	Easy	20
Arrays	New Year Chaos	Medium	40
Arrays	Minimum Swaps 2	Medium	40
Arrays	Array Manipulation	Hard	60
String Manipulation	Strings: Making Anagrams	Easy	25
String Manipulation	Alternating Characters	Easy	20
String Manipulation	Sherlock and the Valid String	Medium	35
String Manipulation	Special String Again	Medium	40

Problem Solving

Subdomain	Challenge	Difficulty	Points	Solution
Warmup	Solve Me First	Easy	1
Warmup	Simple Array Sum	Easy	10
Warmup	Compare the Triplets	Easy	10
Warmup	A Very Big Sum	Easy	10
Warmup	Diagonal Difference	Easy	10
Warmup	Plus Minus	Easy	10
Warmup	Staircase	Easy	10
Warmup	Mini-Max Sum	Easy	10
Warmup	Birthday Cake Candles	Easy	10
Warmup	Time Conversion	Easy	15
Implementation	Grading Students	Easy	10
Implementation	Apple and Orange	Easy	10
Implementation	Kangaroo	Easy	10
Implementation	Between Two Sets	Easy	10
Implementation	Divisible Sum Pairs	Easy	10
Implementation	Bon Appétit	Easy	10
Implementation	Sock Merchant	Easy	10

Java

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

SQL

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

Regex

Subdomain	Challenge	Difficulty	Points	Solution
Introduction	Matching Specific String	Easy	5
Introduction	Matching Anything But a Newline	Easy	5
Introduction	Matching Digits & Non-Digit Characters	Easy	5
Introduction	Matching Whitespace & Non-Whitespace Character	Easy	5
Introduction	Matching Word & Non-Word Character	Easy	5
Introduction	Matching Start & End	Easy	5
Character Class	Matching Specific Characters	Easy	10
Character Class	Excluding Specific Characters	Easy	10
Character Class	Matching Character Ranges	Easy	10
Repetitions	Matching {x} Repetitions	Easy	20
Repetitions	Matching {x, y} Repetitions	Easy	20
Repetitions	Matching Zero Or More Repetitions	Easy	20
Repetitions	Matching One Or More Repetitions	Easy	20
Repetitions	Matching Ending Items	Easy	20
Grouping and Capturing	Matching Word Boundaries	Easy	20
Grouping and Capturing	Capturing & Non-Capturing Groups	Easy	20
Grouping and Capturing	Alternative Matching	Easy	20
Backreferences	Matching Same Text Again & Again	Easy	20
Backreferences	Backreferences To Failed Groups	Easy	20
Backreferences	Branch Reset Groups	Easy	20
Backreferences	Forward References	Easy	20
Assertions	Positive Lookahead	Easy	20
Assertions	Negative Lookahead	Easy	20
Assertions	Positive Lookbehind	Easy	20
Assertions	Negative Lookbehind	Easy	20