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Solutions and visual explanations to HackerRank problems, fully tested using official sample test cases that are not locked behind a paywall.

Problems

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Unofficial listing

Meta Coursework

Visit problem set

Topic 1 — Arrays & String

A Very Big Sum

Designer PDF Viewer

Left Rotation

Topic 2 — Lists

Insert a Node at a Specific Position in a Linked List

Cycle Detection

Topic 3 — Stacks & Queues

Balanced Brackets

Queue using Two Stacks

Topic 4 — Hash & Maps

Ice Cream Parlor

~~Colorful Numbers~~

Topic 5 — Sorting Algorithms

Insertion Sort I

Quicksort II

Topic 6 — Trees

Binary Search Tree: Insertion

Tree: Height of a Binary Tree

QHEAP1

Topic 7 — Graphs (DFS & BFS)

Breadth First Search: Shortest Reach

Snakes and Ladders: The Quickest Way Up

Topic 8 — Recursion

Fibonacci Numbers

Official listing

Algorithms	Data Structures
Solve Me First Simple Array Sum Compare the Triplets A Very Big Sum Diagonal Difference Plus Minus Staircase Mini-Max Sum Birthday Cake Candles Time Conversion Grading Students Apple and Orange Number Line Jumps Between Two Sets Breaking the Records Subarray Division Divisible Sum Pairs Migratory Birds Day of the Programmer Bill Division Sales by Match Drawing Book Counting Valleys Electronic Shop Cats and a Mouse Forming a Magic Square Picking Numbers Climbing the Leaderboard The Hurdle Race Designer PDF Viewer Utopian Tree Angry Professor Beautiful Days at the Movies Viral Advertising Save the Prisoner! Circular Array Rotation Sequence Equation Jumping on the Clouds: Revisited Find Digits Extra Long Factorials Append and Delete Sherlock and Squares Library Fine Cut the Sticks Non-Divisible Subset Repeated String Jumping on the Clouds Equalize the Array Queen's Attack II ACM ICPC Team Taum and B'day Organizing Containers of Balls Encryption Bigger is Greater Modified Kaprekar Numbers Beautiful Triplets Minimum Distances Halloween Sale The Time in Words Chocolate Feast Service Lane Lisa's Workbook Flatland Space Stations Fair Rations Cavity Map Manasa and Stones The Grid Search Happy Ladybugs Strange Counter 3D Surface Area Absolute Permutation The Bomberman Game Ema's Supercomputer Larry's Array Almost Sorted Matrix Layer Rotation Big Sorting Super Reduced String Intro to Tutorial Challenges CamelCase Insertion Sort - Part 1 Strong Password Two Characters Insertion Sort - Part 2 Correctness and the Loop Invariant Caesar Cipher Mars Exploration Running Time of Algorithms HackerRank in a String! Quicksort 1 - Partition Pangrams Weighted Uniform Strings Separate the Numbers Funny String Counting Sort 1 Counting Sort 2 Gemstones Alternating Characters The Full Counting Sort Beautiful Binary String Closest Numbers The Love-Letter Mystery Find the Median Determining DNA Health Insertion Sort Advanced Analysis Palindrome Index Fraudulent Activity Notifications Anagram Making Anagrams Lily's Homework Game of Thrones - I Two Strings String Construction Sherlock and the Valid String Highest Value Palindrome Maximum Palindromes Sherlock and Anagrams Common Child Bear and Steady Gene Morgan and a String Count Strings String Function Calculation Build a Palindrome Build a String Gridland Provinces Cards Permutation Ashton and String String Similarity Super Functional Strings Circular Palindromes Similar Strings Save Humanity Find Strings Palindromic Border Two Two Two Strings Game Letter Islands Pseudo-Isomorphic Substrings How Many Substrings? Hackerland Radio Transmitters Gridland Metro Ice Cream Parlor	Arrays - DS 2D Array - DS Dynamic Array Left Rotation Sparse Arrays Array Manipulation Print the Elements of a Linked List Insert a Node at the Tail of a Linked List Insert a Node at the Head of a Linked List Insert a Node at a Specific Position in a Linked List Delete a Node Print in Reverse Reverse a Linked List Compare Two Linked Lists Merge Two Sorted Linked Lists Get Node Value Delete Duplicate-Value Nodes from a Sorted Linked List Cycle Detection Find Merge Point of Two Lists Inserting a Node Into a Sorted Doubly Linked List Reverse a doubly linked list Tree: Preorder Traversal Tree: Postorder Traversal Tree: Inorder Traversal Tree: Height of a Binary Tree Tree: Top View Tree: Level Order Traversal Binary Search Tree: Insertion Tree: Huffman Decoding Binary Search Tree: Lowest Common Ancestor Swap Nodes [Algo] Kitty's Calculations on a Tree Is This a Binary Search Tree? Square-Ten Tree Balanced Forest Jenny's Subtrees Tree Coordinates Array Pairs Self Balancing Tree Array and simple queries Median Updates Merging Communities QHEAP1 Maximum Element Queue using Two Stacks Components in a Graph Balanced Brackets Castle on the Grid Jesse and Cookies Kundu and Tree Find trhe Running Median Down to Zero II Equal Stacks Minimum Average Waiting Time Truck Tour Game of Two Stacks Largest Rectangle Queries with Fixed Length Super Maximum Cost Queries Simple Text Editor Poisonous Plants AND xor OR Waiter Contacts No Prefix Set Data Structures MCQ 1 Data Structures MCQ 2 Data Structures MCQ 3 Kindergarten Adventures Cube Summation Mr. X and His Shots Direct Connections Subsequence Weighting Jim and the Skycrapers Palindromic Subsets Counting On a Tree Polynomial Division Costly Intervals The Strange Function Self-Driving Bus Unique Colors Fibonacci Numbers Tree Pair Sums Functional Palindromes Lazy White Falcon Ticket to Ride Heavy Light White Falcon Sum of the Maximums Number Game on a Tree Heavy Light 2 White Falcon Library Query Starfleet Almost Equal - Advanced Almost Sorted Interval Burger Happiness Roy and Alpha-Beta Trees Coloring Tree Recalling Early Days GP with Trees Swaps and Sum Arithmetic Progressions Coolguy and Two Subsequences White Falcon And Tree Subtrees And Paths Triples Beautiful Segments Divisibility BST Maintenance Find Maximum Index Product Taxicab Driver's Problem Jaggu Playing with Balloons Dynamic Summation Two Array Problem Rooted Tree The Crazy Helix Network Administration Easy Addition Find the Permutation Company Retreat Box Operations Max Transform Array and Queries

Algorithms

Data Structures

Solve Me First
Simple Array Sum
Compare the Triplets
A Very Big Sum
Diagonal Difference
Plus Minus
Staircase
Mini-Max Sum
Birthday Cake Candles
Time Conversion
Grading Students
Apple and Orange
Number Line Jumps
Between Two Sets
Breaking the Records
Subarray Division
Divisible Sum Pairs
Migratory Birds
Day of the Programmer
Bill Division
Sales by Match
Drawing Book
Counting Valleys
Electronic Shop
Cats and a Mouse
Forming a Magic Square
Picking Numbers
Climbing the Leaderboard
The Hurdle Race
Designer PDF Viewer
Utopian Tree
Angry Professor
Beautiful Days at the Movies
Viral Advertising
Save the Prisoner!
Circular Array Rotation
Sequence Equation
Jumping on the Clouds: Revisited
Find Digits
Extra Long Factorials
Append and Delete
Sherlock and Squares
Library Fine
Cut the Sticks
Non-Divisible Subset
Repeated String
Jumping on the Clouds
Equalize the Array
Queen's Attack II
ACM ICPC Team
Taum and B'day
Organizing Containers of Balls
Encryption
Bigger is Greater
Modified Kaprekar Numbers
Beautiful Triplets
Minimum Distances
Halloween Sale
The Time in Words
Chocolate Feast
Service Lane
Lisa's Workbook
Flatland Space Stations
Fair Rations
Cavity Map
Manasa and Stones
The Grid Search
Happy Ladybugs
Strange Counter
3D Surface Area
Absolute Permutation
The Bomberman Game
Ema's Supercomputer
Larry's Array
Almost Sorted
Matrix Layer Rotation
Big Sorting
Super Reduced String
Intro to Tutorial Challenges
CamelCase
Insertion Sort - Part 1
Strong Password
Two Characters
Insertion Sort - Part 2
Correctness and the Loop Invariant
Caesar Cipher
Mars Exploration
Running Time of Algorithms
HackerRank in a String!
Quicksort 1 - Partition
Pangrams
Weighted Uniform Strings
Separate the Numbers
Funny String
Counting Sort 1
Counting Sort 2
Gemstones
Alternating Characters
The Full Counting Sort
Beautiful Binary String
Closest Numbers
The Love-Letter Mystery
Find the Median
Determining DNA Health
Insertion Sort Advanced Analysis
Palindrome Index
Fraudulent Activity Notifications
Anagram
Making Anagrams
Lily's Homework
Game of Thrones - I
Two Strings
String Construction
Sherlock and the Valid String
Highest Value Palindrome
Maximum Palindromes
Sherlock and Anagrams
Common Child
Bear and Steady Gene
Morgan and a String
Count Strings
String Function Calculation
Build a Palindrome
Build a String
Gridland Provinces
Cards Permutation
Ashton and String
String Similarity
Super Functional Strings
Circular Palindromes
Similar Strings
Save Humanity
Find Strings
Palindromic Border
Two Two
Two Strings Game
Letter Islands
Pseudo-Isomorphic Substrings
How Many Substrings?
Hackerland Radio Transmitters
Gridland Metro
Ice Cream Parlor

Arrays - DS
2D Array - DS
Dynamic Array
Left Rotation
Sparse Arrays
Array Manipulation
Print the Elements of a Linked List
Insert a Node at the Tail of a Linked List
Insert a Node at the Head of a Linked List
Insert a Node at a Specific Position in a Linked List
Delete a Node
Print in Reverse
Reverse a Linked List
Compare Two Linked Lists
Merge Two Sorted Linked Lists
Get Node Value
Delete Duplicate-Value Nodes from a Sorted Linked List
Cycle Detection
Find Merge Point of Two Lists
Inserting a Node Into a Sorted Doubly Linked List
Reverse a doubly linked list
Tree: Preorder Traversal
Tree: Postorder Traversal
Tree: Inorder Traversal
Tree: Height of a Binary Tree
Tree: Top View
Tree: Level Order Traversal
Binary Search Tree: Insertion
Tree: Huffman Decoding
Binary Search Tree: Lowest Common Ancestor
Swap Nodes [Algo]
Kitty's Calculations on a Tree
Is This a Binary Search Tree?
Square-Ten Tree
Balanced Forest
Jenny's Subtrees
Tree Coordinates
Array Pairs
Self Balancing Tree
Array and simple queries
Median Updates
Merging Communities
QHEAP1
Maximum Element
Queue using Two Stacks
Components in a Graph
Balanced Brackets
Castle on the Grid
Jesse and Cookies
Kundu and Tree
Find trhe Running Median
Down to Zero II
Equal Stacks
Minimum Average Waiting Time
Truck Tour
Game of Two Stacks
Largest Rectangle
Queries with Fixed Length
Super Maximum Cost Queries
Simple Text Editor
Poisonous Plants
AND xor OR
Waiter
Contacts
No Prefix Set
Data Structures MCQ 1
Data Structures MCQ 2
Data Structures MCQ 3
Kindergarten Adventures
Cube Summation
Mr. X and His Shots
Direct Connections
Subsequence Weighting
Jim and the Skycrapers
Palindromic Subsets
Counting On a Tree
Polynomial Division
Costly Intervals
The Strange Function
Self-Driving Bus
Unique Colors
Fibonacci Numbers Tree
Pair Sums
Functional Palindromes
Lazy White Falcon
Ticket to Ride
Heavy Light White Falcon
Sum of the Maximums
Number Game on a Tree
Heavy Light 2 White Falcon
Library Query
Starfleet
Almost Equal - Advanced
Almost Sorted Interval
Burger Happiness
Roy and Alpha-Beta Trees
Coloring Tree
Recalling Early Days GP with Trees
Swaps and Sum
Arithmetic Progressions
Coolguy and Two Subsequences
White Falcon And Tree
Subtrees And Paths
Triples
Beautiful Segments
Divisibility
BST Maintenance
Find Maximum Index Product
Taxicab Driver's Problem
Jaggu Playing with Balloons
Dynamic Summation
Two Array Problem
Rooted Tree
The Crazy Helix
Network Administration
Easy Addition
Find the Permutation
Company Retreat
Box Operations
Max Transform
Array and Queries

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