Algorithms
Data structures, and algorithms based questions and solutions with detailed explanation and code. 569+ problems with Java solutions.
Sorting9
Bit Manipulation20
Backtracking20
Binary Search26
Two Pointers22
Sliding Window30
Strings & Hashing47
Arrays & Hashing90
Stack26
Heap / Priority Queue21
Trees34
Dynamic Programming41
Intervals17
Graph39
Union Find15
Trie12
Math20
Greedy25
Design15
Matrix15
Linked List25
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Sorting Algorithms (9)
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Bit Manipulation Based Problems (20)
- Bitwise And Of Numbers Range
- Counting Bits
- Divide Integers
- Find The Difference
- Flip And Invert Image
- Gray Code
- Hamming Distance
- Maximum Product Of Word Lengths
- Maximum Xor Of Two Numbers
- Minimum Flips To Make A Or B Equal C
- Missing Number
- Number Of 1 Bits
- Power Of Two
- Reverse Bits
- Single Number
- Single Number II
- Single Number III
- Sum Of Two Integers
- Total Hamming Distance
- Xor Queries Of Subarray
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Backtracking Based Problems (20)
- All Paths Source Target
- Beautiful Arrangement
- Combination Sum
- Combination Sum II
- Combination Sum III
- Fair Distribution Of Cookies
- Generate Parentheses
- Gray Code
- Letter Case Permutation
- Letter Combinations Of Phone Number
- N Queens
- N Queens II
- Palindrome Partitioning II
- Permutations
- Permutations II
- Restore IP Addresses
- Subsets
- Subsets II
- Sudoku Solver
- Word Search
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Binary Search Based Problems (26)
- Allocate Books
- Arranging Coins
- Binary Search
- Capacity To Ship Package In Ddays
- Find First And Last Position In Sorted Array
- Find Kth Smallest Pair Distance
- Find Minimum In Rotated Sorted Array
- Find Minimum In Rotated Sorted Array II
- Find Peak Element
- Find Right Interval
- Guess Number Higher Lower
- H Index II
- Koko Eating Bananas
- Kth Smallest In Sorted Matrix
- Median Of Two Sorted Arrays
- Minimum Number Of Days To Make M Bouquets
- Minimum Speed To Arrive On Time
- Search A 2 D Matrix
- Search In Rotated Sorted Array
- Search In Rotated Sorted Array II
- Search Insert Position
- Single Element In Sorted Array
- Smallest Divisor Given A Threshold
- Sqrt
- Time Based Key Value Store Bs
- Valid Perfect Square
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Two Pointers Based Problems (22)
- Backspace String Compare
- Container With Most Water
- Count Pairs Whose Sum Less Than Target
- Dutch National Flag
- Find The Duplicate Number
- Long Pressed Name
- Max Consecutive Ones
- Merge Strings
- Minimum Length Of String
- Move Zeroes TP
- Remove Duplicates Sorted Array
- Reverse String TP
- Reverse Vowels Of String
- Reverse Words In String
- Reverse Words In String III
- Sort Array By Parity
- Squares Of Sorted Array TP
- Three Sum
- Trapping Rain Water
- Two Pointers Intro
- Two Sum Sorted
- Valid Palindrome TP
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Sliding Window Based Problems (30)
- Best Time To Buy And Sell Stock
- Contains Duplicates II
- Count Distinct Integers After Reverse Operations
- Find K Closest Elements
- Frequency Of The Most Frequent Element
- Fruits Into Basket
- Longest Repeating Character Replacement
- Longest Sub String With K Distinct Chracters
- Longest Sub String With K Unique Characters
- Longest Subarray Of 1 s After Deleting One Element
- Longest Substring With Atleast K Repeating Chars
- Longest Substring Without Repeating Characters
- Max Consecutive Ones III
- Maximum Average Subarray I
- Maximum Erasure Value
- Maximum Number Of Vowels In Substring Of Given Length
- Maximum Sum Of Subarrays With Equal Sums
- Min Operations To Reduce X To Zero
- Minimum Consecutive Cards To Pick Up
- Minimum Number Of Flips To Make The Binary String Alternate
- Minimum Size Sub Array Sum
- Minimum Window Substring
- Minimum Window Substring II
- Number Of Sub Arrays Of Size K And Avg Greater Than Or Equal To Threshold
- Number Of Substrings Containing All Three Characters
- Number Of Ways To Form Target String
- Permutation In String
- Sliding Window
- Sliding Window Maximum
- Substrings Of Size Three With Distinct Characters
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Strings & Hashing Based Problems (47)
- Basic Calculator II
- Break A String Into Maximum Unique Substrings
- Check If A String Contains All Binary Codes Of Size K
- Count And Say
- Count Binary Substrings
- Count Substrings That Differ By One Character
- Decode String
- Encode And Decode Strings
- Encode Decode Tiny URL
- Find All Anagrams In A String
- Find And Replace In String
- Find The Index Of The First Occurrence In A String
- Group Anagrams
- Integer To Roman
- Is String Has Unique Characters
- Is Subsequence
- Isomorphic Strings
- KMP String Matching
- Length Of Largest Sub String
- Length Of Last Word
- Longest Common Prefix
- Longest Palindrome Subsequence
- Manachers Algorithm
- Maximum Difference Between Node And Ancestor
- Maximum Number Of Balloons
- Maximum Product Of The Length Of Two Palindromic Subsequences
- Merge Strings Alternately
- Minimum Number Of Swaps To Make The String Balanced
- Minimum Window Substring II
- Number Of Substrings Containing All Three Characters
- Optimal Partition Of String
- Repeat String
- Repeated DNA Sequences
- Reverse String
- Reverse Words In String
- Reverse Words In String III
- Roman To Integer
- Rotate String
- Scramble String
- Shortest Palindrome
- Sort Vowels In String
- Unique Length 3 Palindromic Subsequences
- Valid Anagram
- Valid Palindrome
- Valid Palindrome II
- Word Pattern
- Z Function
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Arrays & Hashing Based Problems (90)
- 3 Sum
- 4 Sum
- Array With Elements Not Equal To Average Of Neighbors
- Best Time To Buy And Sell Stock II
- Boats To Save People
- Brick Wall
- Can Place Flowers
- Candy Distribution
- Concatenation Of Array
- Container With Most Water
- Contains Duplicates
- Continuous Subarray Sum
- Count Number Of Texts
- Count Subarrays With K Different Integers
- Design Hash Map
- Design Hash Set
- Design Parking System
- Design Underground System
- Dota 2 Senate
- Find Kth Largest
- Find Missing Numbers From Array
- Find Pivot Index
- Find The Difference Of Two Arrays
- First Missing Positive
- Four Sum II
- Gas Station
- Grid Game
- Insert Delete Get Random
- Jump Game
- Jump Game II
- K Frequent Elements
- Kth Missing Positive Number
- Largest Number
- Largest Rectangle Matrix
- Longest Consecutive Sequence
- Majority Element
- Make Array Strictly Increasing
- Max Chunks To Make Sorted
- Max Consecutive Ones III
- Maximum Number Of Coins You Can Get
- Maximum Number Of Tasks You Can Assign
- Maximum Profit In Job Scheduling
- Maximum Sum Circular Subarray
- Maximum Sum Of 3 Non Overlapping Subarrays
- Maximum Sum Subarray
- Maximum Width Ramp
- Median Of Two Sorted Arrays Of Diff Size
- Median Of Two Sorted Arrays Of Same Size
- Merge Sorted Array
- Mimimum Operations To Make Array Continuous
- Minimum Diff Between Highest And Lowest Of K Scores
- Minimum Jumps To Reach Home
- Minimum Penalty For A Shop
- Minimum Size Subarray Sum
- Move Zeroes
- Naming A Company
- Next Greater Element 1
- Non Decreasing Array
- Number Of Pairs Of Interchangeable Rectangles
- Number Of Subsequences That Satisfy Target Sum Condition
- Number Of Ways To Split Array
- Number Of Zero Filled Subarrays
- Pascals Triangle
- Product Of Array Except Self
- Push Dominoes
- Range Sum Query 2 D Immutable
- Range Sum Query Immutable
- Remove Duplicates From Sorted Array
- Remove Duplicates From Sorted Array II
- Remove Element
- Replace Elements With Greatest From Right
- Replacing Ones With K
- Rotate Array
- Set Matrix Zeroes
- Shortest Subarray With Sum At Least K
- Sign Of An Array
- Sort Colors
- Spiral Order Matrix
- Squares Of Sorted Array
- Stock Span
- Subarray Sum Equals K
- Sum Of Subarray Minimums
- Text Justification
- Transpose Matrix
- Trapping Rain Water
- Two Sum
- Two Sum II
- Unique Email Addresses
- Validate Sudoku
- Wiggle Sort
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Stack Based Problems (26)
- 132 Pattern
- Asteroid Collision
- Baseball Game
- Car Fleet
- Daily Temperatures
- Decode String
- Exclusive Time Of Functions
- Largest Rectangle In Histogram
- Max Stack
- Maximum Frequency Stack
- Min Add To Make Parentheses Valid
- Min Remove To Make Valid Parentheses
- Min Stack
- Monotonic Stack Intro
- Next Greater Element II
- Online Stock Span
- Remove All Adjacent Duplicates In String II
- Remove K Digits
- Removing Stars From String
- Reverse Polish Notation
- Simplify Path
- Stack Using Queue
- Sum Of Subarray Minimums
- Trapping Rain Water Using Stack
- Valid Parentheses
- Validate Stack Sequences
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Heap / Priority Queue Based Problems (21)
- Course Schedule III
- Farthest Building You Can Reach Heap
- Find Kth Largest In Stream
- Find Median From Data Stream
- Heap Intro
- IPO
- Kth Largest Element
- Kth Largest In Stream
- Maximum Subsequence Score
- Meeting Rooms II Heap
- Merge K Sorted Lists
- Minimum Cost To Connect Points
- Minimum Cost To Connect Sticks
- Minimum Cost To Hire K Workers
- Reorganize String Heap
- Sliding Window Median
- Smallest Number In Infinite Set
- Smallest Range From K Lists
- Sort Characters By Frequency
- Task Scheduler Heap
- Top K Frequent Elements
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Trees Based Problems (34)
- All Nodes Distance K In Binary Tree
- Average Of Levels
- Balanced Binary Tree
- Binary Tree Maximum Path Sum
- Binary Tree Paths
- Binary Tree Right Side View
- Construct Binary Tree From Inorder Postorder
- Construct Binary Tree From Preorder Inorder
- Count Good Nodes In Binary Tree
- Delete Node In BST
- Diameter Of Binary Tree
- Flatten Binary Tree To Linked List
- Insert Into BST
- Invert Binary Tree
- Kth Smallest Element In BST
- Level Order Traversal
- Lowest Common Ancestor
- Lowest Common Ancestor BST
- Max Depth Binary Tree
- Maximum Difference Between Node And Ancestor
- Maximum Width Of Binary Tree
- Path Sum
- Path Sum II
- Path Sum III
- Populating Next Right Pointers
- Recover BST
- Same Tree
- Serialize Deserialize Binary Tree
- Sum Of Left Leaves
- Symmetric Tree
- Trees Intro
- Validate BST
- Vertical Order Traversal Of Binary Tree
- Zigzag Level Order Traversal
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Dynamic Programming Based Problems (41)
- Best Time Buy Sell Stock III
- Best Time Buy Sell Stock IV
- Best Time Buy Sell Stock With Cooldown
- Best Time Buy Sell Stock With Transaction Fee
- Climbing Stairs
- Coin Change
- Decode Ways
- Delete And Earn
- Distinct Subsequences
- Dungeon Game
- Edit Distance
- House Robber
- House Robber 2
- Interleaving String
- Intro
- Jump Game
- Jump Game II
- Largest Divisible Subset
- Longest Common Subsequence
- Longest Increasing Subsequence
- Longest Palindrome String
- Max Product Sub Array
- Maximal Square
- Min Cost Climbing Stairs
- Minimum Falling Path Sum
- Minimum Path Sum
- Nth Tribonacci Number
- Number Of Longest Increasing Subsequences
- Palindromic Substrings
- Partition Equal Subset
- Perfect Squares
- Regular Expression Matching
- Robot Unique Paths Obstacles
- Scramble String
- Target Sum
- Triangle Min Path Sum
- Unique Paths
- Unique Paths II
- Video Stitching
- Wildcard Matching
- Word Break
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Intervals Based Problems (17)
- Car Pooling
- Data Stream As Disjoint Intervals
- Employee Free Time
- Insert Interval
- Interval List Intersections
- Meeting Rooms
- Meeting Rooms II
- Merge Intervals
- Minimum Arrows To Burst Balloons
- Minimum Number Of Days To Make M Bouquets
- My Calendar I
- Non Overlapping Intervals
- Remove Covered Intervals
- Sliding Window Median
- Smallest Range From K Lists
- Split Array Into Consecutive Subsequences
- Video Stitching
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Graph Based Problems (39)
- Alien Dictionary
- All Ancestors Of Node In DAG
- BFS
- Cheapest Flights Within K Stops
- Clone Graph
- Course Schedule
- Critical Connections In Network
- DFS
- Dijkstra
- Find Eventual Safe States
- Graph Intro
- Graph Valid Tree
- Keys And Rooms
- Kruskal
- Longest Path With Different Adjacent Characters
- Making A Large Island
- Max Area Of Island
- Minesweeper
- Minimum Cost To Connect Points
- Minimum Height Trees
- Network Delay Time
- Number Of Closed Islands
- Number Of Connected Components
- Number Of Enclaves
- Number Of Islands
- Number Of Operations To Make Network Connected
- Pacific Atlantic Water Flow
- Parallel Courses
- Prim
- Reconstruct Itinerary
- Rotting Oranges
- Satisfiability Of Equality Equations
- Shortest Path BFS
- Shortest Path In Binary Matrix
- Surrounded Regions
- Topological Sort
- Walls And Gates
- Word Ladder
- Word Ladder II
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Union Find Based Problems (15)
- Accounts Merge
- Graph Valid Tree
- Largest Component Size By Common Factor
- Making A Large Island
- Minimum Cost To Connect Points
- Minimum Spanning Tree Kruskal
- Number Of Connected Components
- Number Of Operations To Make Network Connected
- Number Of Operations To Make Network Connected 2
- Number Of Provinces
- Redundant Connection
- Regions Cut By Slashes
- Satisfiability Of Equality Equations
- Smallest String With Swaps
- Surrounded Regions
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Math Based Problems (20)
- Add Strings
- Bulb Switcher
- Count Primes
- Divide Two Integers
- Excel Sheet Column Number
- Excel Sheet Column Title
- Fizz Buzz
- Happy Number
- Minimum Moves To Equal Array Elements
- Multiply Strings
- Nth Tribonacci Number
- Nth Ugly Number
- Palindrome Number
- Power Of Four
- Power Of Three
- Prime Arrangements
- Random Pick With Weight
- Reverse Integer
- Strobogrammatic Number
- Ugly Number
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Greedy Based Problems (25)
- Assign Cookies
- Boat To Save People Greedy
- Car Pooling
- Course Schedule III
- Delete Columns To Make Sorted
- Farthest Building You Can Reach
- Gas Station
- Hand Of Straights
- Jump Game
- Jump Game II
- Lemonade Change
- Maximum Swap
- Maximum Units On A Truck
- Minimum Cost To Connect Sticks
- Minimum Domino Rotations For Equal Row
- Minimum Number Of Refueling Stops
- Minimum Number Of Taps To Water Garden
- Partition Labels
- Queue Reconstruction By Height
- Remove Duplicate Letters
- Reorganize String
- Smallest Range From K Lists Greedy
- Task Scheduler
- Two City Scheduling
- Wiggle Subsequence
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Design Based Problems (15)
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Matrix Based Problems (15)
- Count Negative Numbers In Sorted Matrix
- Flood Fill
- Game Of Life
- Longest Increasing Path In Matrix
- Maximal Rectangle
- Minesweeper
- Pacific Atlantic Water Flow
- Rotate Image
- Search A 2 D Matrix
- Search A 2 D Matrix II
- Set Matrix Zeroes
- Shortest Path In Binary Matrix
- Spiral Matrix
- Spiral Matrix II
- Walls And Gates
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Linked List Based Problems (25)
- Add Two Numbers
- Add Two Numbers II
- Copy List With Random Pointer
- Delete Node In Linked List
- Flatten Multilevel Doubly Linked List
- Intersection Of Two Linked Lists
- LFU Cache
- LRU Cache
- Linked List Cycle
- Linked List Cycle II
- Merge Two Sorted Lists
- Merge Two Sorted Lists And Remove Duplicates
- Middle Of Linked List
- Odd Even Linked List
- Palindrome Linked List
- Partition List
- Remove Duplicates From Sorted List
- Remove Nth Node From End Of List
- Reorder List
- Reverse Linked List
- Reverse Linked List II
- Reverse Nodes In K Group
- Rotate List
- Sort List
- Swap Nodes In Pairs