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Core CS

General Programming

Basic Programming
Object-Oriented Programming
RegEx

Algorithms

Sorting
Search
Greedy Algorithms
Graph Theory
Strings
Dynamic Programming
Bit Manipulation
Recursion

Implementation

Brute-Force

Debugging

Missing Lines

DataStructures

Arrays
Linked Lists
Trees
Balanced Trees
Stacks
Queues
Heap
Disjoint Set
Multiple Choice
Trie
Advanced

Math

Fundamentals
Number Theory
Combinatorics
Algebra
Geometry
Probability
Linear Algebra Foundations

Languages

C++

Introduction
Strings
Classes
STL
Inheritance
Other Concepts

Java

Introduction
Strings
BigNumber
Data Structures
Object Oriented Programming
Exception Handling
Advanced

Python

Introduction
Classes
Basic Data Types
Strings
Python Functionals
Regex and Parsing
XML
Closures and Decorators
Sets
Math
Itertools
Collections
Date and Time
Errors and Exceptions
Numpy

Solutions

Basic Programming

Title	Solution	Time	Space	Difficulty	Points	Note
Solve Me First	Java	O(1)	O(1)	Easy	1
Staircase	Java	O(n)	O(n)	Easy	10
Plus Minus	Java	O(n)	O(1)	Easy	10
Diagonal Difference	Java	O(n^2)	O(1)	Easy	10
A Very Big Sum	Java	O(n)	O(1)	Easy	10
Simple Array Sum	Java	O(n)	O(1)	Easy	10
Compare the Triplets	Java	O(1)	O(1)	Easy	10
Divisible Sum Pairs	Java	O(n^2)	O(n)	Easy	10
Kangaroo	Java	O(1)	O(1)	Easy	10
Drawing Book	Java			Easy	10
Birthday Cake Candles	Java	O(n)	O(1)	Easy	10
Bon Appetit	Java			Easy	10
Sock Merchant	Java			Easy	10
Apple and Orange	Java			Easy	10
Between Two Sets	Java	O((A^2)+B)	O(1)	Easy	10
Mini-Max Sum	Java	O(1)	O(1)	Easy	10
Grading Students	Java	O(n)	O(1)	Easy	10
Breaking the Records	Java	O(n)	O(1)	Easy	10
Migratory Birds	Java			Easy	10
Birthday Chocolate	Java	O(n)	O(1)	Easy	10
Time Conversion	Java	O(1)	O(1)	Easy	15
Library Fine	Java			Easy	15
Save the Prisoner!	Java			Easy	15
Jumping on the Clouds: Revisited	Java			Easy	15
Counting Valleys	Java	O(n)	O(1)	Easy	15
Viral Advertising	Java			Easy	15
Beautiful Days at the Movies	Java			Easy	15
Electronics Shop	Java	O(n log (n))	O(1)	Easy	15	n = m+n
Cats and a Mouse	Java	O(1)	O(1)	Easy	15
The Hurdle Race	Java	O(n)	O(1)	Easy	15
Utopian Tree	Java			Easy	20
Service Lane	Java			Easy	20
Circular Array Rotation	Java			Easy	20
Sherlock and Squares	Java			Easy	20
Angry Professor	Java			Easy	20
Extra Long Factorials	Java			Medium	20
Minimum Distances	Java			Easy	20
Non-Divisible Subset	Java			Medium	20
Beautiful Triplets	Java			Easy	20
Jumping on the Clouds	Java			Easy	20
Equalize the Array	Java			Easy	20
Designer PDF Viewer	Java			Easy	20
Magic Square Forming	Java			Easy	20
Repeated String	Java			Easy	20
Bitwise AND	Java			Easy	20
Divisible Pairs Sum	Java			Easy	20
Append and Delete	Java			Easy	20
Picking Numbers	Java	O(n)	O(n)	Easy	20
Climbing the Leaderboard	Java	O(n+m)	(n)	Easy	20
Sequence Equation	Java	O(n)	O(n)	Easy	20
Find Digits	Java			Easy	25
Chocolate Feast	Java			Easy	25
Cut the sticks	Java			Easy	25
ACM ICPC Team	Java			Easy	25
Taum and B'day	Java			Easy	25
The Time in Words	Java			Medium	25
Flatland Space Stations	Java			Easy	25
Lisa's Workbook	Java			Easy	25
Fair Rations	Java			Easy	25
Manasa and Stones	Java			Easy	30
Cavity Map	Java			Easy	30
The Grid Search	Java			Medium	30
Happy Ladybugs	Java			Easy	30
Strange Counter	Java			Easy	30
Consecutive 1's in Binary Numbers	Java			Easy	30
Nested Logic	Java			Easy	30

Object-Oriented Programming

Title	Solution	Time	Space	Difficulty	Points
Class vs. Instance	Java			Easy	30
Inheritance	Java	O(n)	O(1)	Easy	30
Abstract Classes	Java			Easy	30

RegEx

Title	Solution	Time	Space	Difficulty	Points
UK and US: Part 2	Java			Easy	10
Alien Username	Java			Easy	10
Detect HTML Tags	Java			Easy	10
Detect HTML links	Java			Easy	10
Find A Sub-Word	Java			Easy	10
IP Address Validation	Java			Easy	10
Find HackerRank	Java			Easy	15
The British and American Style of Spelling	Java			Easy	15
Split the Phone Numbers	Java			Easy	15
Valid PAN format	Java			Easy	15
Saying Hi	Java			Easy	15
HackerRank Tweets	Java			Easy	15
HackerRank Language	Java			Easy	15
Utopian Identification Number	Java			Easy	15
Find a Word	Java			Medium	15
Build a Stack Exchange Scraper	Java			Easy	15
Detect the Domain Name	Java			Medium	15
Detect the Email Addresses	Java			Medium	15
Detect HTML Attributes	Java			Easy	20
HackerRank in a String!	Java	O(n)	O(1)	Easy	20
Building a Smart IDE: Programming Language Detection	Java			Medium	30
Count Strings	Java			Hard	80

Sorting

Title	Solution	Time	Space	Difficulty	Points
Intro to Tutorial Challenges	Java	O(n)	O(1)	Easy	30
Insertion Sort - Part 1	Java	O(n)	O(1)	Easy	30
Insertion Sort - Part 2	Java	O(n^2)	O(1)	Easy	30
Insertion Sort Advanced Analysis	Java			Advanced	50
Correctness and the Loop Invariant	Java	O(n^2)	O(1)	Easy	30
Running Time of Algorithms	Java	O(n^2)	O(1)	Easy	30
Quicksort 1 - Partition	Java	O(n)	O(n)	Easy	10
Quicksort 2 - Sorting	Java	O(n^2)	O(n)	Easy	30
Quicksort In-Place	Java	O(n^2)	O(log(n))	Medium	35
Running Time of Quicksort	Java	O(n log(n))	O(log(n))	Easy	35
Counting Sort 1	Java	O(n+k)	O(k)	Easy	30
Counting Sort 2	Java	O(n+k)	O(k)	Easy	30
Counting Sort 3	Java	O(n+k)	O(k)	Easy	30
The Full Counting Sort	Java	O(n+k)	O(k)	Medium	40
Marc's Cakewalk	Java	O(n + k)	O(k)	Easy	15
Minimum Absolute Difference in an Array	Java	O(n log(n))	O(1)	Easy	15
Organizing Containers of Balls	Java	O(n^2)	O(n^2)	Medium	30
Find the Median	Java	O(n log(n))	O(n)	Easy	35
Closest Numbers	Java	O(n log(n))	O(n)	Easy	35
Mark and Toys	Java	O(n log(n))	O(n)	Easy	35
Permuting Two Arrays	Java	O(n log (n))	O(n)	Easy	40
Jim and the Orders	Java	O(n log (n))	O(n)	Easy	40
Fraudulent Activity Notifications	Java	O(n^2)	O(n)	Medium	40
Lily's Homework	Java	O(n log(n))	O(n)	Medium	40
Merge Sort: Counting Inversions	Java			Hard	45
Mr. X and His Shots	Java			Medium	50
Super Maximum Cost Queries	Java			Hard	60
GCD Matrix	Java			Hard	60
A Super Hero	Java			Hard	80
Functional Palindromes	Java			Advanced	80
Super Functional Strings	Java			Advanced	80
Sorted Subsegments	Java			Hard	80

Search

Title	Solution	Time	Space	Difficulty	Points
Hackerland Radio Transmitters	JS	O(n log(n))	O(1)	Easy	15
Lonely Integer	Java	O(n)	O(1)	Easy	20
Bit Manipulation: Lonely Integer	Java	O(n)	O(1)	Easy	20
Gridland Metro	Java			Medium	25
Ice Cream Parlor	Java	O(n)	O(n)	Easy	30
Greedy Florist	Java			Medium	35
Find the Median	Java	O(n log(n))	O(n)	Easy	35
Closest Numbers	Java	O(n log(n))	O(n)	Easy	35
Binary Search: Ice Cream Parlor	Java	O(n)	O(n)	Easy	35
Minimum Loss	Java	O(n log(n))	O(n)	Medium	35
KnightL on a Chessboard	Java			Medium	35
Sherlock and Array	Java C++	O(n)	O(n)	Easy	40
Short Palindrome	Java			Medium	40
Missing Numbers	Java			Easy	45
Making Candies	Java			Hard	45
DFS: Connected Cell in a Grid	Java			hard	45
Pairs	Java			Medium	50
Count Luck	Java			Medium	50
Cut the Tree	Java			Medium	50
Connected Cells in a grid	Java			Medium	50
Gena Playing Hanoi	Java			Medium	50
Beautiful Quadruples	Java			Medium	50
Coin on the Table	Java			Medium	65
Interval Selection	Java			Medium	65
Bike Racers	Java			Hard	65
Maximum Subarray Sum	Java			Hard	65
Task Scheduling	Java			Advanced	70
Queens on Board	Java			Hard	70
Median Updates	Java			Hard	70
Similar Pair	Java			Advanced	70
Absolute Element Sums	Java			Hard	70
Maximizing Mission Points	Java			Hard	70
Arithmetic Progressions	Java			Advanced	80
Billboards	Java			Advanced	80
Requirement	Java			Advanced	80
King Richard's Knights	Java			Hard	80
Sorted Subsegments	Java			Hard	80
Distant Pairs	Java			Expert	80
Triplets	Java			Medium	20
Spies, Revised	Java			Expert	100
TBS Problem	Java			Expert	100

Greedy Algorithms

Title	Solution	Time	Space	Difficulty	Points
Two Characters	Java	O(n)	O(1)	Easy	15
Marc's Cakewalk	Java	O(n + k)	O(k)	Easy	15
Grid Challenge	Java	O(n(n log (n)))*	O(n^2)	Easy	20
Luck Balance	Java	O(n log(n))	O(1)	Easy	20
Maximum Perimeter Triangle	Java	O(n log (n))	O(n)	Easy	20
Equal Stacks	Java	O(n)	O(n)	Easy	25
Sherlock and The Beast	Java	O(n)	O(n)	Easy	30
Priyanka and Toys	Java	O(n log(n))	O(n)	Easy	30
Largest Permutation	Java			Easy	30
Beautiful Pairs	Java			Easy	30
Yet Another Minimax Problem	Java			Medium	20
Flipping the Matrix	Java	O(n^2)	O(n^2)	Medium	30
Roads and Libraries	Java			Medium	30
Greedy Florist	Java			Medium	35
Mark and Toys	Java	O(n log(n))	O(n)	Easy	35
Max Min	Java			Medium	35
Permuting Two Arrays	Java			Easy	40
Jim and the Orders	Java			Easy	40
Goodland Electricity	Java			Medium	40
Fun Game	Java			Medium	40
Reverse Shuffle Merge	Java			Advanced	50
Cutting Boards	Java			Hard	60
Algorithmic Crush	Java			Hard	60
Prim's (MST): Special Subtree	Java			Medium	60
Accessory Collection	Java			Hard	60
Chief Hopper	Java	O(n)	O(n)	Hard	65
Sherlock and MiniMax	Java			Hard	70
Team Formation	Java			Advanced	70

Graph Theory

Title	Solution	Time	Space	Difficulty	Points
Roads and Libraries	Java			Medium	30
Synchronous Shopping	Java			Medium	40
Crab Graphs	Java			Medium	50
Even Tree	Java			Medium	50
Snakes and Ladders: THe Quickest Way Up	Java			Medium	50
Subset Component	Java			Hard	50
Journey to the Moon	Java Python 3	O(n + i)	O(n)	Medium	50
Kruskal (MST): Really Special Subtree	Java			Hard	50
Minimum Penalty Path	Java			Medium	50
Demanding Money	Java			Hard	50

Strings

Title	Solution	Time	Space	Difficulty	Points
Super Reduced String	Java			Easy	10
camelCase	Java			Easy	15
Two Characters	Java	O(n)	O(1)	Easy	15
Caesar Cipher	Java			Easy	15
Mars Exploration	Java			Easy	15
Weighted Uniform Strings	Java			Easy	20
Separate the Numbers	Java			Easy	20
Funny String	Java			Easy	25
Gemstones	Java			Easy	20
Alternating Characters	Java			Easy	20
Beautiful Binary String	Java			Easy	20
The Love-Letter Mystery	Java	O(n)	O(1)	Easy	20
Determining DNA Health	Java			Hard	50
Palindrome Index	Java			Easy	25
Anagram	Java	O(n)	O(1)	Easy	25
Game of Thrones - I	Java	O(n)	O(1)	Easy	30
Two Strings	Java	O(\|a\| + \|b\|)	O(1)	Easy	25
String Construction	Java			Easy	25
Sherlock and Valid String	Java	O(n)	O(n)	Hard	100
Richie Rich	Java			Medium	30
Sherlock and Anagrams	Java			Medium	50
Common Child	Java			Hard	60
Bear and Steady Gene	Java			Medium	50
Morgan and a String	Java			Expert	100
Count Strings	Java			Hard	80
String Function Calculation	Java			Advanced	80
Build a Palindrome	Java			Advanced	80
Build a String	Java			Hard	80
Gridland Provinces	Java			Hard	80
Ashton and String	Java			Advanced	100
String Similarity	Java			Expert	100
Super Functional Strings	Java			Advanced	80
Circular Palindromes	Java			Advanced	120
Similar Strings	Java			Advanced	85
Save Humanity	Java			Expert	100
Find Strings	Java			Expert	100
Palindromic Border	Java			Expert	100
Two Two	Java			Advanced	150
Two Strings Game	Java			Expert	100
Letter Islands	Java			Expert	100
Pseudo-Isomorphic Substrings	Java			Expert	100
How Many Substrings?	Java			Expert	100

Dynamic Programming

Title	Solution	Difficulty	Points
Equal	Java	Medium	30
Cut Tree	Java	Medium	40
Mr K marsh	Java	Medium	40
Sam and sub-strings	Java	Medium	40
Summing Pieces	Java	Medium	40
Short Palindrome	Java	Medium	40
Abbreviation	Java	Medium	40
Fair Cut	Java	Medium	40
Fibonacci Modified	Java	Medium	45
Lego Blocks	Java	Medium	50
Candies	Java	Medium	50
Stock Maximize	Java	Medium	50
Angry Childtren 2	Java	Hard	50
The Maximum Subarray	Java	Medium	50
Sherlock and Cost	Java	Medium	50
Xor and Sum	Java	Medium	50
Counting Special Sub-Cubes	Java	Medium	50
Two Robots	Java	Medium	50
Kingdom Division	Java	Medium	50
Prime XOR	Java	Medium	50
HackerRank City	Java	Medium	50
Nikita and the Game	Java	Medium	50
Prime Digit Sums	Java	Medium	50
Mandragora Forest	Java	Medium	50
LCS Returns	Java	Medium	50
Grid Walking	Java	Medium	55
Bricks Game	Java	Medium	55
The Longest Common Subsequence	Java	Medium	55
Substring Diff	Java	Medium	60
Brick Tiling	Java	Hard	60
Alien Languages	Java	Hard	60
The Longest Increasing Subsequence	Java	Advanced	60
The Coin Change Problem	Java	Hard	60
Knapsack	Java	Medium	60
Sherlock's Array Merging Algorithm	Java	Hard	60
New Year Game	Java	Medium	60
Shashank and the Palindromic Strings	Java	Advanced	60
Decibinary Numbers	Java	Hard	60
Choosing White Balls	Java	Hard	60
DP: Coin Change	Java	Hard	60
Clues on a Binary Path	Java	Hard	60
GCD Matrix	Java	Hard	60
Coin on the Table	Java	Medium	65
Interval Selection	Java	Medium	65
Red John is Back	Java	Medium	65
Play with words	Java	Medium	65
Queens on Board	Java	Hard	70
String Reduction	Java	Hard	70
Far Vertices	Java	Hard	70
The Indian Job	Java	Medium	70
Hexagonal Grid	Java	Hard	70
Longest Palindromic Subsequence	Java	Hard	70
Turn Off the Lights	Java	Hard	70
Tara's Beautiful Permutations	Java	Hard	70
Two Subarrays	Java	Expert	70
Mining	Java	Advanced	75
The Longest Common Subsequence (LCS)	Java	Hard	75
Points in a Plane	Java	Advanced	80
Fairy Chess	Java	Advanced	80
Billboards	Java	Advanced	80
Requirement	Java	Advanced	80
A Super Hero	Java	Hard	80
Covering the stains	Java	Hard	80
Superman Celebrates Diwali	Java	Hard	80
Wet Shark and Two Subsequences	Java	Medium	80
Zurikela's Graph	Java	Hard	80
New Year Present	Java	Hard	80
Suffix Rotation	Java	Expert	80
Black and White Tree	Java	Hard	80
Beautiful Strings	Java	Hard	80
Longest Mod Path	Java	Hard	80
Super Functional Strings	Java	Advanced	80
Kitty's Calculations on a Tree	Java	Advanced	80
Liars	Java	Advanced	85
Dorsey Thief	Java	Advanced	85
Swap Permutation	Java	Medium	85
Candles Counting	Java	Medium	85
Square Subsequences	Java	Hard	90
Hyper Strings	Java	Advanced	90
Unique Divide And Conquer	Java	Advanced	90
Super Kth LIS	Java	Advanced	90
Counting Road Networks	Java	Expert	90
Lucky Numbers	Java	Expert	100
Count Scorecards	Java	Expert	100
Unfair Game	Java	Advanced	100
Oil Well	Java	Hard	100
Modify The Sequence	Java	Advanced	100
Divisible Numbers	Java	Expert	100
Ones and Twos	Java	Hard	100
Extremum Permutations	Java	Medium	100
Tree Pruning	Java	Advanced	100
P-sequences	Java	Hard	100
Best spot	Java	Advanced	100
Find the Seed	Java	Advanced	100
The Blacklist	Java	Advanced	100
Police Operation	Java	Hard	100
Road Maintenance	Java	Hard	100
King and Four Sons	Java	Expert	100
Counting the Ways	Java	Expert	100
Hard Disk Drives	Java	Expert	100
Travel around the world	Java	Medium	120
Robot	Java	Advanced	120
Vim War	Java	Advanced	120
Dortmund Dilemma	Java	Advanced	150
Separate the chocolate	Java	Expert	250

Bit Manipulation

#	Title	Solution	Time	Space	Difficulty	Points	Note

Recursion

Title	Solution	Difficulty	Points
The Power Sum	Java	Easy	20
Crossword Puzzle	Java	Medium	30
Recursive Digit Sum	Java	Medium	30
Simplified Chess Engine	Java	Medium	40
Password Cracker	Java	Medium	40
Artithmetic Expressions	Java	Hard	40
K Factorization	Java	Hard	50
Bowling Pins	Java	Advanced	60
Simplified Chess Engine II	Java	Hard	60
Repetitive K-Sums	Java	Advanced	150

Constructive Algorithms

Title	Solution	Time	Space	Difficulty	Points
Lena Sort	Java			Medium	30
Flipping the Matrix	Java	O(n^2)	O(n^2)	Medium	30
Gaming Array	Java			Medium	35
New Year Chaos	Java			Medium	40
Bonetrousle	Java			Medium	50
Yet Another KMP Problem	Java			Hard	60
Beautiful 3 Set	Java			Hard	60
Inverse RMQ	Java			Hard	60
Two Subarrays	Java			Expert	70
Lovely Triplets	Java			Advanced	80
Array Construction	Java			Advanced	80

Brute-Force

Title	Solution	Time	Space	Difficulty	Points
Pangrams	Java			Easy	20
Climbing the Leaderboard	Java	O(n+m)	(n)	Easy	20
Strings: Making Anagrams	Java	O(\|a\|+\|b\|)	O(1)	Easy	30
Enryption	Java			Medium	30
Making Anagrams	Java			Easy	30
Modified Kaprekar Numbers	Java			Easy	30
Queen's Attack II	Java	O(k)	O(1)	Medium	30
Organizing Containers of Balls	Java	O(n^2)	O(n^2)	Medium	30
Bigger is Greater	Java			Medium	35
Ema's Supercomputer	Java			Medium	40
Absolute Permuation	Java			Medium	40
Larry's Array	Java			Medium	40
The Bomberman Game	Java	O(nm)*	O(nm)*	Medium	40
Almost Sorted	Java			Medium	50
Beautiful Quadruples	Java			Medium	50
HackerRank City	Java			Medium	50
Maximixing the Function	Java			Hard	70
Matrix Layer Rotation	Java			Hard	80
Gridland Provinces	Java			Hard	80
Fighting Pits	Java			Hard	80
Find the permutation	Java			Expert	150

Missing Lines

#	Title	Solution	Time	Space	Difficulty	Points	Note
	Lonely Integer - Fill the key-line	Java			Easy	20
	Make It Anagram	Java			Easy	20

Data Structures

Arrays

#	Title	Solution	Time	Space	Difficulty	Points	Note

Stacks

#	Title	Solution	Time	Space	Difficulty	Points	Note

Trees

#	Title	Solution	Time	Space	Difficulty	Points	Note

Linked Lists

#	Title	Solution	Time	Space	Difficulty	Points	Note
	Compare two linked lists	C++	O(n)	O(1)	Easy	5

Graphs

#	Title	Solution	Time	Space	Difficulty	Points	Note

Tries

#	Title	Solution	Time	Space	Difficulty	Points	Note

Queues

#	Title	Solution	Time	Space	Difficulty	Points	Note

Suffix Array

#	Title	Solution	Time	Space	Difficulty	Points	Note

Heaps

#	Title	Solution	Time	Space	Difficulty	Points	Note

Disjoint Set

#	Title	Solution	Time	Space	Difficulty	Points	Note

Math

Number Theory

#	Title	Solution	Time	Space	Difficulty	Points	Note

Game Theory

#	Title	Solution	Time	Space	Difficulty	Points	Note

Geometry

#	Title	Solution	Time	Space	Difficulty	Points	Note

Algebra

#	Title	Solution	Time	Space	Difficulty	Points	Note

Fundamentals

#	Title	Solution	Time	Space	Difficulty	Points	Note

Combinatorics

#	Title	Solution	Time	Space	Difficulty	Points	Note

Probability

#	Title	Solution	Time	Space	Difficulty	Points	Note

| | Walking the Approximate Longest Path| Java | | | Hard | 70 | || | | Sam's Puzzle (Approximate)| Java | | | Advanced | 85 | || | | Java Substring| Java | O(1) | O(1) | Easy | 5 | ||

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Core CS

General Programming

Algorithms

Implementation

Debugging

DataStructures

Math

Languages

C++

Java

Python

Solutions

Basic Programming

Object-Oriented Programming

RegEx

Sorting

Search

Greedy Algorithms

Graph Theory

Strings

Dynamic Programming

Bit Manipulation

Recursion

Constructive Algorithms

Brute-Force

Missing Lines

Data Structures

Arrays

Stacks

Trees

Linked Lists

Graphs

Tries

Queues

Suffix Array

Heaps

Disjoint Set

Math

Number Theory

Game Theory

Geometry

Algebra

Fundamentals

Combinatorics

Probability