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All Lessons
Free Lessons (187)
Getting Started
Course Overview
Who Should Take This Course
Two Pointers
Introduction to Two Pointers
Valid Palindrome
Solution: Valid Palindrome
3Sum
Solution: 3Sum
Remove Nth Node from End of List
Solution: Remove Nth Node from End of List
Sort Colors
Solution: Sort Colors
Reverse Words in a String
Solution: Reverse Words in a String
Valid Word Abbreviation
Solution: Valid Word Abbreviation
Strobogrammatic Number
Solution: Strobogrammatic Number
Minimum Number of Moves to Make Palindrome
Solution: Minimum Number of Moves to Make Palindrome
Next Palindrome Using Same Digits
Solution: Next Palindrome Using Same Digits
Lowest Common Ancestor of a Binary Tree III
Solution: Lowest Common Ancestor of a Binary Tree III
Count Pairs Whose Sum is Less than Target
Solution: Count Pairs Whose Sum is Less than Target
Valid Palindrome II
Mock interview
Two Pointers
Fast and Slow Pointers
Introduction to Fast and Slow Pointers
Happy Number
Solution: Happy Number
Linked List Cycle
Solution: Linked List Cycle
Middle of the Linked List
Solution: Middle of the Linked List
Circular Array Loop
Solution: Circular Array Loop
Find the Duplicate Number
Solution: Find the Duplicate Number
Palindrome Linked List
Solution: Palindrome Linked List
Maximum Twin Sum of a Linked List
Solution: Maximum Twin Sum of a Linked List
Split a Circular Linked List
Solution: Split a Circular Linked List
Linked List Cycle III
Solution: Linked List Cycle III
Mock interview
Fast and Slow Pointers
Sliding Window
Introduction to Sliding Window
Repeated DNA Sequences
Solution: Repeated DNA Sequences
Sliding Window Maximum
Solution: Sliding Window Maximum
Minimum Window Subsequence
Solution: Minimum Window Subsequence
Longest Repeating Character Replacement
Solution: Longest Repeating Character Replacement
Minimum Window Substring
Solution: Minimum Window Substring
Longest Substring without Repeating Characters
Solution: Longest Substring without Repeating Characters
Minimum Size Subarray Sum
Solution: Minimum Size Subarray Sum
Maximum Average Subarray I
Solution: Maximum Average Subarray I
Diet Plan Performance
Solution: Diet Plan Performance
Fruit Into Baskets
Solution: Fruit Into Baskets
Contains Duplicate II
Solution: Contains Duplicate II
Frequency of the Most Frequent Element
Solution: Frequency of the Most Frequent Element
Mock interview
Sliding Window
Merge Intervals
Introduction to Merge Intervals
Merge Intervals
Solution: Merge Intervals
Insert Interval
Solution: Insert Interval
Interval List Intersections
Solution: Interval List Intersections
Employee Free Time
Solution: Employee Free Time
Count Days Without Meetings
Solution: Count Days Without Meetings
Meeting Rooms II
In-Place Manipulation of a Linked List
Introduction to In-Place Manipulation of a Linked List
Reverse Linked List
Solution: Reverse Linked List
Reverse Nodes in k-Group
Solution: Reverse Nodes in k-Group
Reverse Linked List II
Solution: Reverse Linked List II
Reorder List
Solution: Reorder List
Swapping Nodes in a Linked List
Solution: Swapping Nodes in a Linked List
Reverse Nodes in Even Length Groups
Solution: Reverse Nodes in Even Length Groups
Remove Duplicates from Sorted List
Solution: Remove Duplicates from Sorted List
Remove Linked List Elements
Solution: Remove Linked List Elements
Split Linked List in Parts
Solution: Split Linked List in Parts
Delete N Nodes After M Nodes of a Linked List
Solution: Delete N Nodes After M Nodes of a Linked List
Swap Nodes in Pairs
Heaps
Introduction to Heaps
IPO
Solution: IPO
Find Median from Data Stream
Solution: Find Median from Data Stream
Sliding Window Median
Solution: Sliding Window Median
Schedule Tasks on Minimum Machines
Solution: Schedule Tasks on Minimum Machines
Meeting Rooms III
Solution: Meeting Rooms III
Largest Number After Digit Swaps by Parity
Solution: Largest Number After Digit Swaps by Parity
Find Right Interval
Solution: Find Right Interval
Minimum Cost to Connect Sticks
Solution: Minimum Cost to Connect Sticks
Longest Happy String
Solution: Longest Happy String
Maximum Average Pass Ratio
Solution: Maximum Average Pass Ratio
The Number of the Smallest Unoccupied Chair
Solution: The Number of the Smallest Unoccupied Chair
Mock interview
Heaps
K-way merge
Introduction to K-way Merge
Merge Sorted Array
Solution: Merge Sorted Array
Kth Smallest Number in M Sorted Lists
Solution: Kth Smallest Number in M Sorted Lists
Find K Pairs with Smallest Sums
Solution: Find K Pairs with Smallest Sums
Merge K Sorted Lists
Solution: Merge K Sorted Lists
Kth Smallest Element in a Sorted Matrix
Solution: Kth Smallest Element in a Sorted Matrix
Kth Smallest Prime Fraction
Solution: Kth Smallest Prime Fraction
Super Ugly Number
Solution: Super Ugly Number
Top K Elements
Introduction to Top K Elements
Kth Largest Element in a Stream
Solution: Kth Largest Element in a Stream
Reorganize String
Solution: Reorganize String
K Closest Points to Origin
Solution: K Closest Points to Origin
Top K Frequent Elements
Solution: Top K Frequent Elements
Kth Largest Element in an Array
Solution: Kth Largest Element in an Array
Third Maximum Number
Solution: Third Maximum Number
Find Subsequence of Length K with the Largest Sum
Solution: Find Subsequence of Length K with the Largest Sum
Minimum Cost to Hire K Workers
Solution: Minimum Cost to Hire K Workers
Maximal Score After Applying K Operations
Solution: Maximal Score After Applying K Operations
Find the Kth Largest Integer in the Array
Solution: Find the Kth Largest Integer in the Array
Modified Binary Search
Introduction to Modified Binary Search
Binary Search
Solution: Binary Search
Search in Rotated Sorted Array
Solution: Search in Rotated Sorted Array
First Bad Version
Solution: First Bad Version
Random Pick with Weight
Solution: Random Pick with Weight
Find K Closest Elements
Solution: Find K Closest Elements
Single Element in a Sorted Array
Solution: Single Element in a Sorted Array
Maximum Value at a Given Index in a Bounded Array
Solution: Maximum Value at a Given Index in a Bounded Array
The K Weakest Rows in a Matrix
Solution: The K Weakest Rows in a Matrix
Split Array Largest Sum
Solution: Split Array Largest Sum
Search in Rotated Sorted Array II
Mock interview
Modified Binary Search
Subsets
Introduction to Subsets
Subsets
Solution: Subsets
Permutations
Solution: Permutations
Letter Combinations of a Phone Number
Solution: Letter Combinations of a Phone Number
Generate Parentheses
Solution: Generate Parentheses
Letter Case Permutation
Solution: Letter Case Permutation
Find K-Sum Subsets
Greedy Techniques
Introduction to Greedy Techniques
Jump Game
Solution: Jump Game
Boats to Save People
Solution: Boats to Save People
Gas Station
Solution: Gas Station
Two City Scheduling
Solution: Two City Scheduling
Minimum Number of Refueling Stops
Solution: Minimum Number of Refueling Stops
Largest Palindromic Number
Solution: Largest Palindromic Number
Assign Cookies
Solution: Assign Cookies
Rearranging Fruits
Solution: Rearranging Fruits
Number of Steps to Reduce a Binary Number to One
Solution: Number of Steps to Reduce a Binary Number to One
Maximum Swap
Solution: Maximum Swap
Can Place Flowers
Solution: Can Place Flowers
Largest Odd Number in String
Solution: Largest Odd Number in String
Jump Game II
Best Time to Buy and Sell Stock
Backtracking
Introduction to Backtracking
N-Queens
Solution: N-Queens
Word Search
Solution: Word Search
House Robber III
Solution: House Robber III
Restore IP Addresses
Solution: Restore IP Addresses
Flood Fill
Solution: Flood Fill
Minimum Moves to Spread Stones Over Grid
Solution: Minimum Moves to Spread Stones Over Grid
Binary Tree Paths
Solution: Binary Tree Paths
Binary Watch
Solution: Binary Watch
Optimal Account Balancing
Solution: Optimal Account Balancing
Split a String Into the Max Number of Unique Substrings
Solution: Split a String Into the Max Number of Unique Substrings
Sudoku Solver
Matchsticks to Square
Dynamic Programming
Introduction to Dynamic Programming
0/1 Knapsack
Solution: 0/1 Knapsack
Coin Change
Solution: Coin Change
N-th Tribonacci Number
Solution: N-th Tribonacci Number
Partition Equal Subset Sum
Solution: Partition Equal Subset Sum
Counting Bits
Solution: Counting Bits
01 Matrix
Solution: 01 Matrix
House Robber II
Solution: House Robber II
Maximum Product Subarray
Solution: Maximum Product Subarray
Combination Sum
Solution: Combination Sum
Word Break
Solution: Word Break
Palindromic Substrings
Solution: Palindromic Substrings
Longest Common Subsequence
Solution: Longest Common Subsequence
Word Break II
Solution: Word Break II
Decode Ways
Solution: Decode Ways
Count the Number of Good Subsequences
Solution: Count the Number of Good Subsequences
Climbing Stairs
Mock interview
Dynamic Programming
Cyclic Sort
Introduction to Cyclic Sort
Missing Number
Solution: Missing Number
First Missing Positive
Solution: First Missing Positive
Find the Corrupt Pair
Solution: Find the Corrupt Pair
Find the First K Missing Positive Numbers
Sort Array By Parity II
Solution: Sort Array By Parity II
Topological Sort
Introduction to Topological Sort
Compilation Order
Solution: Compilation Order
Alien Dictionary
Solution: Alien Dictionary
Verifying an Alien Dictionary
Solution: Verifying an Alien Dictionary
Course Schedule II
Solution: Course Schedule II
Course Schedule
Solution: Course Schedule
Build a Matrix with Conditions
Solution: Build a Matrix with Conditions
Longest Path With Different Adjacent Characters
Solution: Longest Path With Different Adjacent Characters
Find All Possible Recipes from Given Supplies
Mock interview
Topological Sort
Sort and Search
Introduction to Sort and Search
Find the Distance Value Between Two Arrays
Solution: Find the Distance Value Between Two Arrays
Longest Subsequence With Limited Sum
Solution: Longest Subsequence With Limited Sum
Find Target Indices After Sorting Array
Solution: Find Target Indices After Sorting Array
Count Pairs in Two Arrays
Solution: Count Pairs in Two Arrays
Valid Triangle Number
Solution: Valid Triangle Number
Minimum Operations to Make All Array Elements Equal
Solution: Minimum Operations to Make All Array Elements Equal
Sum of Mutated Array Closest to Target
Solution: Sum of Mutated Array Closest to Target
Range Sum of Sorted Subarray Sums
Solution: Range Sum of Sorted Subarray Sums
Magnetic Force Between Two Balls
Solution: Magnetic Force Between Two Balls
Find K-th Smallest Pair Distance
Solution: Find K-th Smallest Pair Distance
Minimum Space Wasted from Packaging
Solution: Minimum Space Wasted from Packaging
Russian Doll Envelopes
Solution: Russian Doll Envelopes
Two Sum Less Than K
Maximum Number of Integers to Choose from a Range I
Matrices
Introduction to Matrices
Set Matrix Zeroes
Solution: Set Matrix Zeroes
Rotate Image
Solution: Rotate Image
Spiral Matrix
Solution: Spiral Matrix
Where Will the Ball Fall
Solution: Where Will the Ball Fall
Transpose Matrix
Solution: Transpose Matrix
Count Negative Numbers in a Sorted Matrix
Solution: Count Negative Numbers in a Sorted Matrix
Minimum Time Takes to Reach Destination Without Drowning
Solution:Minimum Time Takes to Reach Destination Without Drowning
Smallest Rectangle Enclosing Black Pixels
Solution: Smallest Rectangle Enclosing Black Pixels
Island Perimeter
Solution: Island Perimeter
Convert 1D Array Into 2D Array
Solution: Convert 1D Array Into 2D Array
Spiral Matrix II
Solution: Spiral Matrix II
Flip Columns For Maximum Number of Equal Rows
Solution: Flip Columns For Maximum Number of Equal Rows
Number of Spaces Cleaning Robot Cleaned
Solution: Number of Spaces Cleaning Robot Cleaned
Stacks
Introduction to Stacks
Basic Calculator
Solution: Basic Calculator
Remove All Adjacent Duplicates In String
Solution: Remove All Adjacent Duplicates In String
Minimum Remove to Make Valid Parentheses
Solution: Minimum Remove to Make Valid Parentheses
Exclusive Time of Functions
Solution: Exclusive Time of Functions
Flatten Nested List Iterator
Solution: Flatten Nested List Iterator
Implement Queue Using Stacks
Solution: Implement Queue Using Stacks
Daily Temperatures
Solution: Daily Temperatures
Decode String
Solution: Decode String
Minimum String Length After Removing Substrings
Solution: Minimum String Length After Removing Substrings
Valid Parentheses
Graphs
Introduction to Graphs
Network Delay Time
Solution: Network Delay Time
Paths in Maze That Lead to Same Room
Solution: Paths in Maze That Lead to Same Room
Clone Graph
Solution: Clone Graph
Graph Valid Tree
Solution: Graph Valid Tree
Bus Routes
Solution: Bus Routes
Reconstruct Itinerary
Solution: Reconstruct Itinerary
Find the Town Judge
Solution: Find the Town Judge
Find Center of Star Graph
Solution: Find Center of Star Graph
Lucky Numbers in a Matrix
Solution: Lucky Numbers in a Matrix
Path with Maximum Probability
Solution: Path with Maximum Probability
Mock interview
Graphs
Tree Depth-First Search
Introduction to Tree Depth-First Search
Flatten Binary Tree to Linked List
Solution: Flatten Binary Tree to Linked List
Diameter of Binary Tree
Solution: Diameter of Binary Tree
Serialize and Deserialize Binary Tree
Solution: Serialize and Deserialize Binary Tree
Invert Binary Tree
Solution: Invert Binary Tree
Binary Tree Maximum Path Sum
Solution: Binary Tree Maximum Path Sum
Convert Sorted Array to Binary Search Tree
Solution: Convert Sorted Array to Binary Search Tree
Build Binary Tree from Preorder and Inorder Traversal
Solution: Build Binary Tree from Preorder and Inorder Traversal
Binary Tree Right Side View
Solution: Binary Tree Right Side View
Lowest Common Ancestor of a Binary Tree
Solution: Lowest Common Ancestor of a Binary Tree
Validate Binary Search Tree
Solution: Validate Binary Search Tree
Nested List Weight Sum II
Solution: Nested List Weight Sum II
Inorder Successor in BST
Solution: Inorder Successor in BST
Height of Binary Tree After Subtree Removal Queries
Solution: Height of Binary Tree After Subtree Removal Queries
Delete Nodes And Return Forest
Solution: Delete Nodes And Return Forest
Maximum Depth of Binary Tree
Kth Smallest Element in a BST
Tree Breadth-First Search
Introduction to Tree Breadth-First Search
Binary Tree Level Order Traversal
Solution: Binary Tree Level Order Traversal
Binary Tree Zigzag Level Order Traversal
Solution: Binary Tree Zigzag Level Order Traversal
Populating Next Right Pointers in Each Node
Solution: Populating Next Right Pointers in Each Node
Vertical Order Traversal of a Binary Tree
Solution: Vertical Order Traversal of a Binary Tree
Symmetric Tree
Solution: Symmetric Tree
Word Ladder
Solution: Word Ladder
Two Sum IV – Input Is a BST
Solution: Two Sum IV – Input Is a BST
Connect All Siblings of a Binary Tree
Mock interview
Tree Breadth First Search
Trie
Introduction to Trie
Implement Trie (Prefix Tree)
Solution: Implement Trie (Prefix Tree)
Search Suggestions System
Solution: Search Suggestions System
Replace Words
Solution: Replace Words
Design Add and Search Words Data Structure
Solution: Design Add and Search Words Data Structure
Word Search II
Solution: Word Search II
Top K Frequent Words
Solution: Top K Frequent Words
Longest Common Prefix
Solution: Longest Common Prefix
Index Pairs of a String
Solution: Index Pairs of a String
Lexicographical Numbers
Hash Maps
Introduction to Hash Maps
Design HashMap
Solution: Design HashMap
Fraction to Recurring Decimal
Solution: Fraction to Recurring Decimal
Logger Rate Limiter
Solution: Logger Rate Limiter
Next Greater Element I
Solution: Next Greater Element I
Isomorphic Strings
Solution: Isomorphic Strings
Find Duplicate File in System
Solution: Find Duplicate File in System
Dot Product of Two Sparse Vectors
Solution: Dot Product of Two Sparse Vectors
High Five
Solution: High Five
Bulls and Cows
Solution: Bulls and Cows
Custom Sort String
Solution: Custom Sort String
Number of Distinct Islands
Solution: Number of Distinct Islands
Number of Wonderful Substrings
Solution: Number of Wonderful Substrings
Total Appeal of a String
Solution: Total Appeal of a String
Continuous Subarray Sum
Solution: Continuous Subarray Sum
Unique Number of Occurrences
Solution: Unique Number of Occurrences
Longest Palindrome
Knowing What to Track
Introduction to Knowing What to Track
Palindrome Permutation
Solution: Palindrome Permutation
Valid Anagram
Solution: Valid Anagram
Design Tic-Tac-Toe
Solution: Design Tic-Tac-Toe
Group Anagrams
Solution: Group Anagrams
Maximum Frequency Stack
Solution: Maximum Frequency Stack
First Unique Character in a String
Solution: First Unique Character in a String
Find All Anagrams in a String
Solution: Find All Anagrams in a String
Longest Palindrome by Concatenating Two-Letter Words
Solution: Longest Palindrome by Concatenating Two-Letter Words
Rank Teams by Votes
Solution: Rank Teams by Votes
Pairs of Songs With Total Durations Divisible by 60
Solution: Pairs of Songs With Total Durations Divisible by 60
Minimum Number of Pushes to Type Word II
Solution: Minimum Number of Pushes to Type Word II
Task Scheduler
Solution: Task Scheduler
Ransom Note
Union Find
Introduction to Union Find
Redundant Connection
Solution: Redundant Connection
Number of Islands
Solution: Number of Islands
Most Stones Removed with Same Row or Column
Solution: Most Stones Removed with Same Row or Column
Longest Consecutive Sequence
Solution: Longest Consecutive Sequence
Last Day Where You Can Still Cross
Solution: Last Day Where You Can Still Cross
Regions Cut by Slashes
Solution: Regions Cut by Slashes
Accounts Merge
Solution: Accounts Merge
Minimize Malware Spread
Solution: Minimize Malware Spread
Find if Path Exists in Graph
Solution: Find if Path Exists in Graph
The Skyline Problem
Solution: The Skyline Problem
Evaluate Division
Mock interview
Union Find
Custom Data Structures
Introduction to Custom Data Structures
Snapshot Array
Solution: Snapshot Array
Time Based Key-Value Store
Solution: Time Based Key-Value Store
LRU Cache
Solution: LRU Cache
Insert Delete GetRandom O(1)
Solution: Insert Delete GetRandom O(1)
Min Stack
Solution: Min Stack
Range Module
Solution: Range Module
Shortest Word Distance II
Solution: Shortest Word Distance II
Design HashSet
Solution: Design HashSet
Max Stack
Solution: Max Stack
Moving Average from Data Stream
Solution: Moving Average from Data Stream
Two Sum III - Data structure design
Solution: Two Sum III - Data structure design
Range Sum Query - Immutable
Solution: Range Sum Query - Immutable
LFU Cache
Bitwise Manipulation
Introduction to Bitwise Manipulation
Find the Difference
Solution: Find the Difference
Complement of Base 10 Integer
Solution: Complement of Base 10 Integer
Flipping an Image
Solution: Flipping an Image
Single Number
Solution: Single Number
Single Number II
Solution: Single Number II
Encode and Decode Strings
Solution: Encode and Decode Strings
Sum of All Subset XOR Totals
Solution: Sum of All Subset XOR Totals
Find The K-th Lucky Number
Solution: Find The K-th Lucky Number
Minimum Number of K Consecutive Bit Flips
Solution: Minimum Number of K Consecutive Bit Flips
Find the Longest Substring Having Vowels in Even Counts
Solution: Find the Longest Substring Having Vowels in Even Counts
Count Triplets That Can Form Two Arrays of Equal XOR
Solution: Count Triplets That Can Form Two Arrays of Equal XOR
Longest Subarray With Maximum Bitwise AND
Solution: Longest Subarray With Maximum Bitwise AND
Reverse Bits
Math and Geometry
Introduction to Math and Geometry
Check If It Is a Straight Line
Solution: Check If It Is a Straight Line
Minimum Cuts to Divide a Circle
Solution: Minimum Cuts to Divide a Circle
Rectangle Overlap
Solution: Rectangle Overlap
Minimum Time Visiting All Points
Solution: Minimum Time Visiting All Points
Reverse Integer
Solution: Reverse Integer
Valid Square
Solution: Valid Square
Rectangle Area
Solution: Rectangle Area
Minimum Area Rectangle
Solution: Minimum Area Rectangle
Maximum Area Rectangle With Point Constraints I
Solution: Maximum Area Rectangle With Point Constraints I
Convex Polygon
Solution: Convex Polygon
Queries on Number of Points Inside a Circle
Solution: Queries on Number of Points Inside a Circle
Max Points on a Line
Solution: Max Points on a Line
Maximum Number of Visible Points
Solution: Maximum Number of Visible Points
Minimize Manhattan Distances
Solution: Minimize Manhattan Distances
Minimum Number of Lines to Cover Points
Detonate the Maximum Bombs
Challenge Yourself
Challenge Yourself: Introduction
Shortest Bridge
Number of Connected Components in an Undirected Graph
Median of Two Sorted Arrays
Pacific Atlantic Water Flow
Contains Duplicate
Maximum Subarray
Two Sum
Find Minimum in Rotated Sorted Array
Non-overlapping Intervals
Meeting Rooms
Largest Rectangle in Histogram
Subtree of Another Tree
Sort List
Number of 1 Bits
Container with Most Water
Evaluate Reverse Polish Notation
4Sum
Loud and Rich
Product of Array Except Self
Longest Increasing Subsequence
Sum of Two Integers
Majority Element
Unique Paths
Longest Palindromic Substring
Permutations II
Number of Provinces
Linked List Cycle II
Minimum Flips to Make the Binary String Alternate
Lemonade Change
House Robber
Find All Numbers Disappeared in an Array
Find All Duplicates in an Array
Same Tree
Design In-Memory File System
Design File System
Asteroid Collision
Rotting Oranges
Add Binary
Multiply Strings
Conclusion
Where to Go from Here?
Mock interview
Coding Patterns
Practice Mock Interview
Grokking the Coding Interview Patterns in Python
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