Solutions to problems on HackerRank.

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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

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	Note
	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	Note
	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	Note
	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	Note
	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	Note
	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	Note
	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	Note
	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	Time	Space	Difficulty	Points	Note
	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	Time	Space	Difficulty	Points	Note
	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	Note
	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	Note
	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(n*m)	O(n*m)	Medium	40
	Almost Sorted	Java			Medium	50
	Beautiful Quadruples	Java			Medium	50
	HackerRank City	Java			Medium	50
	Maximizing 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 | ||