LeetCode by Swift

LeetCode Online Judge is a website containing many algorithm questions. Most of them are real interview questions of Google, Facebook, LinkedIn, Apple, etc. This repo shows my solutions by Swift with the code style strictly follows the RayWenderlich Swift Style Guide. Please feel free to reference and STAR to support this repo, thank you!

Progress

Problem Status shows the latest progress to all 1000+ questions. Currently we have 400+ completed solutions. Note: questions with ♥ mark means that you have to Subscript to premium membership of LeetCode to unlock them.

Contributors

Data Structures

• Array
• String
• Linked List
• Stack
• Queue
• Tree
• Dynamic programming
• Depth-first search
• Breadth-first search
• Math
• Search
• Sort
• Graph
• Design

Companies

• Google
• Facebook
• Snapchat
• Uber
• Airbnb
• LinkedIn
• Amazon
• Microsoft

Array

Title	Solution	Difficulty	Time	Space
Verify an Alien Dictionary	Swift	Easy	O(n)	O(n)
Sort Array By Parity	Swift	Easy	O(n)	O(n)
Max Consecutive Ones	Swift	Easy	O(n)	O(1)
Heaters	Swift	Easy	O(nlogn)	O(1)
Number of Boomerangs	Swift	Easy	O(n ^ 2)	O(n)
Island Perimeter	Swift	Easy	O(nm)	O(1)
Majority Element	Swift	Easy	O(n)	O(1)
Majority Element II	Swift	Medium	O(n)	O(1)
First Missing Positive	Swift	Hard	O(n)	O(n)
Intersection of Two Arrays	Swift	Easy	O(n)	O(n)
Intersection of Two Arrays II	Swift	Easy	O(n)	O(n)
Contains Duplicate	Swift	Easy	O(n)	O(n)
Contains Duplicate II	Swift	Easy	O(n)	O(n)
Remove Duplicates from Sorted Array	Swift	Easy	O(n)	O(1)
Remove Duplicates from Sorted Array II	Swift	Medium	O(n)	O(1)
Move Zeroes	Swift	Easy	O(n)	O(1)
Remove Element	Swift	Easy	O(n)	O(1)
Strobogrammatic Number	Swift	Easy	O(n)	O(1)
Can Place Flowers	Swift	Easy	O(n)	O(1)
Two Sum	Swift	Easy	O(n)	O(n)
Two Sum II - Input array is sorted	Swift	Easy	O(n)	O(1)
Two Sum III - Data structure design	Swift	Easy	O(n)	O(1)
Two Sum Less Than K	Swift	Easy	O(nlogn)	O(n)
3Sum	Swift	Medium	O(n^2)	O(nC3)
3Sum Closest	Swift	Medium	O(n^2)	O(nC3)
4Sum	Swift	Medium	O(n^3)	O(nC4)
Increasing Triplet Subsequence	Swift	Medium	O(n)	O(1)
Summary Ranges	Swift	Medium	O(n)	O(n)
Range Sum Query 2D - Immutable	Swift	Medium	O(mn)	O(mn)
Missing Ranges	Swift	Medium	O(n)	O(1)
Asteroid Collision	Swift	Medium	O(n)	O(n)
Maximize Distance to Closest Person	Swift	Easy	O(n)	O(1)
Exam Room	Swift	Medium	O(n)	O(n)
Shortest Word Distance	Swift	Easy	O(n)	O(1)
Shortest Word Distance II	Swift	Medium	O(n)	O(n)
Shortest Word Distance III	Swift	Medium	O(n)	O(1)
Minimum Size Subarray Sum	Swift	Medium	O(n)	O(1)
Maximum Size Subarray Sum Equals k	Swift	Medium	O(n)	O(n)
Smallest Range	Swift	Hard	O(nm)	O(nm)
Product of Array Except Self	Swift	Medium	O(n)	O(1)
Rotate Array	Swift	Easy	O(n)	O(1)
Rotate Image	Swift	Medium	O(n^2)	O(1)
Spiral Matrix	Swift	Medium	O(n^2)	O(1)
Spiral Matrix II	Swift	Medium	O(n^2)	O(1)
Diagonal Traverse	Swift	Medium	O(mn)	O(1)
Valid Sudoku	Swift	Easy	O(n^2)	O(n)
Set Matrix Zero	Swift	Medium	O(n^2)	O(1)
Next Permutation	Swift	Medium	O(n)	O(1)
Gas Station	Swift	Medium	O(n)	O(1)
Game of Life	Swift	Medium	O(n)	O(1)
Task Scheduler	Swift	Medium	O(nlogn)	O(n)
Validate IP Address	Swift	Medium	O(n)	O(1)
Sliding Window Maximum	Swift	Hard	O(n)	O(n)
Longest Consecutive Sequence	Swift	Hard	O(n)	O(n)
Create Maximum Number	Swift	Hard	O(n^2)	O(n)
Find All Numbers Disappeared in an Array	Swift	Easy	O(n)	O(1)

String

Title	Solution	Difficulty	Time	Space
Fizz Buzz	Swift	Easy	O(n)	O(1)
First Unique Character in a String	Swift	Easy	O(n)	O(1)
Keyboard Row	Swift	Easy	O(nm)	O(n)
Valid Word Abbreviation	Swift	Easy	O(n)	O(n)
Valid Palindrome	Swift	Easy	O(n)	O(n)
Valid Palindrome II	Swift	Easy	O(n)	O(n)
Detect Capital	Swift	Easy	O(n)	O(1)
Count and Say	Swift	Easy	O(n^2)	O(1)
Flip Game	Swift	Easy	O(n)	O(n)
Implement strStr()	Swift	Easy	O(nm)	O(n)
Isomorphic Strings	Swift	Easy	O(n)	O(n)
Reverse String	Swift	Easy	O(n)	O(n)
Reverse String II	Swift	Easy	O(n)	O(n)
Reverse Vowels of a String	Swift	Easy	O(n)	O(n)
Reverse Words in a String	Swift	Medium	O(n)	O(1)
Reverse Words in a String II	Swift	Medium	O(n)	O(1)
Reverse Words in a String III	Swift	Easy	O(n)	O(1)
Length of Last Word	Swift	Easy	O(n)	O(n)
String Compression	Swift	Easy	O(n)	O(1)
Add Strings	Swift	Easy	O(n)	O(1)
Shortest Distance to a Character	Swift	Easy	O(n)	O(1)
Multiply Strings	Swift	Medium	O(n)	O(1)
Palindrome Permutation	Swift	Easy	O(n)	O(n)
Valid Anagram	Swift	Easy	O(n)	O(n)
Ransom Note	Swift	Easy	O(n)	O(n)
Group Anagrams	Swift	Medium	O(nmlogm + nlogn)	O(n)
Find Duplicate File in System	Swift	Medium	O(nm)	O(n)
Longest Common Prefix	Swift	Easy	O(nm)	O(m)
Longest Substring Without Repeating Characters	Swift	Medium	O(n)	O(n)
One Edit Distance	Swift	Medium	O(n)	O(n)
Word Pattern	Swift	Easy	O(n)	O(n)
Permutation in String	Swift	Medium	O(nm)	O(n)
Find All Anagrams in a String	Swift	Medium	O(n)	O(n)
Minimum Window Substring	Swift	Hard	O(n^2)	O(n)
Longest Substring with At Most Two Distinct Characters	Swift	Hard	O(n)	O(n)
Longest Substring with At Most K Distinct Characters	Swift	Hard	O(n)	O(n)
Text Justification	Swift	Hard	O(n)	O(n)
Find the Closest Palindrome	Swift	Hard	O(n)	O(n)

Linked List

Title	Solution	Difficulty	Time	Space
Reverse Linked List	Swift	Easy	O(n)	O(1)
Palindrome Linked List	Swift	Easy	O(n)	O(1)
Swap Nodes in Pairs	Swift	Easy	O(n)	O(1)
Remove Linked List Elements	Swift	Easy	O(n)	O(1)
Remove Duplicates from Sorted List	Swift	Easy	O(n)	O(1)
Remove Duplicates from Sorted List II	Swift	Medium	O(n)	O(1)
Remove Nth Node From End of List	Swift	Easy	O(n)	O(1)
Odd Even Linked List	Swift	Medium	O(n)	O(1)
Rotate List	Swift	Medium	O(n)	O(1)
Reorder List	Swift	Medium	O(n)	O(1)
Merge Two Sorted Lists	Swift	Easy	O(n)	O(1)
Merge k Sorted Lists	Swift	Hard	O(mlogn)	O(1)
Partition List	Swift	Medium	O(n)	O(1)
Reverse Nodes in k-Group	Swift	Hard	O(n)	O(1)
LRU Cache	Swift	Hard	O(1)	O(1)
LFU Cache	Swift	Hard	O(1)	O(1)

Stack

Title	Solution	Difficulty	Time	Space
Min Stack	Swift	Easy	O(1)	O(n)
Max Stack	Swift	Easy	O(n)	O(n)
Valid Parentheses	Swift	Easy	O(n)	O(n)
Longest Valid Parentheses	Swift	Hard	O(n)	O(n)
Evaluate Reverse Polish Notation	Swift	Medium	O(n)	O(n)
Exclusive Time of Functions	Swift	Medium	O(n)	O(n)
Simplify Path	Swift	Medium	O(n)	O(n)
Remove K Digits	Swift	Medium	O(n)	O(n)
Ternary Expression Parser	Swift	Medium	O(n)	O(n)
Binary Tree Preorder Traversal	Swift	Medium	O(n)	O(n)
Binary Tree Inorder Traversal	Swift	Medium	O(n)	O(n)
Binary Search Tree Iterator	Swift	Medium	O(n)	O(n)
Binary Tree Postorder Traversal	Swift	Hard	O(n)	O(n)
Decode String	Swift	Medium	O(n)	O(n)
Basic Calculator	Swift	Hard	O(n)	O(n)

Queue

Title	Solution	Difficulty	Time	Space
Implement Queue using Stacks	Swift	Easy	O(n)	O(n)

Tree

Title	Solution	Difficulty	Time	Space
Same Tree	Swift	Easy	O(n)	O(n)
Symmetric Tree	Swift	Easy	O(n)	O(n)
Invert Binary Tree	Swift	Easy	O(n)	O(n)
Binary Tree Upside Down	Swift	Medium	O(n)	O(1)
Minimum Depth of Binary Tree	Swift	Easy	O(n)	O(1)
Maximum Depth of Binary Tree	Swift	Easy	O(n)	O(1)
Diameter of Binary Tree	Swift	Easy	O(n)	O(1)
Balanced Binary Tree	Swift	Easy	O(n)	O(n)
Sum of Left Leaves	Swift	Easy	O(n)	O(1)
Flatten Binary Tree to Linked List	Swift	Medium	O(n)	O(1)
Convert Sorted Array to Binary Search Tree	Swift	Easy	O(n)	O(1)
Validate Binary Search Tree	Swift	Medium	O(n)	O(log n)
Binary Tree Level Order Traversal	Swift	Easy	O(n)	O(n)
Binary Tree Level Order Traversal II	Swift	Easy	O(n)	O(n)
Merge Two Binary Trees	Swift	Easy	O(n)	O(n)
Binary Tree Zigzag Level Order Traversal	Swift	Medium	O(n)	O(n)
Binary Tree Vertical Order Traversal	Swift	Medium	O(n)	O(n)
Kth Smallest Element in a BST	Swift	Medium	O(n)	O(n)
Binary Tree Right Side View	Swift	Medium	O(n)	O(n)
Construct Binary Tree from Preorder and Inorder Traversal	Swift	Medium	O(nlogn)	O(1)
Construct Binary Tree from Inorder and Postorder Traversal	Swift	Medium	O(nlogn)	O(1)
Path Sum	Swift	Easy	O(n)	O(n)
Path Sum II	Swift	Medium	O(n)	O(n)
Path Sum III	Swift	Easy	O(n^2)	O(1)
Binary Tree Paths	Swift	Easy	O(n)	O(n)
Binary Tree Maximum Path Sum	Swift	Hard	O(n)	O(1)
House Robber III	Swift	Medium	O(n)	O(1)
Unique Binary Search Trees	Swift	Medium	O(n^2)	O(n)
Recover Binary Search Tree	Swift	Hard	O(n)	O(1)
Serialize and Deserialize Binary Tree	Swift	Hard	O(n)	O(n)
Serialize and Deserialize N-ary Tree	Swift	Hard	O(n)	O(n)

Dynamic programming

Title	Solution	Difficulty	Time	Space
Nested List Weight Sum	Swift	Easy	O(n)	O(1)
Climbing Stairs	Swift	Easy	O(n)	O(1)
Min Cost Climbing Stairs	Swift	Easy	O(n)	O(n)
Unique Paths	Swift	Medium	O(mn)	O(mn)
Unique Paths II	Swift	Medium	O(mn)	O(mn)
Nested List Weight Sum II	Swift	Medium	O(n)	O(n)
Flip Game II	Swift	Medium	O(n)	O(n)
Can I Win	Swift	Medium	O(2^n)	O(n)
Decode Ways	Swift	Medium	O(n)	O(n)
Minimum Path Sum	Swift	Medium	O(mn)	O(mn)
Generate Parentheses	Swift	Medium	O(2^n)	O(n)
Different Ways to Add Parentheses	Swift	Medium	O(n^n)	O(n)
Best Time to Buy and Sell Stock	Swift	Easy	O(n)	O(1)
Best Time to Buy and Sell Stock II	Swift	Medium	O(n)	O(1)
Best Time to Buy and Sell Stock III	Swift	Hard	O(n)	O(n)
Best Time to Buy and Sell Stock IV	Swift	Hard	O(n^2)	O(n)
Best Time to Buy and Sell Stock with Cooldown	Swift	Medium	O(n^2)	O(n)
Maximum Sum of 3 Non-Overlapping Subarrays	Swift	Hard	O(n)	O(n)
Coin Change	Swift	Medium	O(n^2)	O(n)
Coin Change II	Swift	Medium	O(n^2)	O(n)
Paint House	Swift	Easy	O(n)	O(n)
Paint House II	Swift	Hard	O(n)	O(1)
Longest Increasing Subsequence	Swift	Medium	O(nlogn)	O(n)
Longest Common Subsequence	Swift	Medium	O(mn)	O(1)
Palindromic Substrings	Swift	Medium	O(n^2)	O(n^2)
Longest Palindromic Substring	Swift	Medium	O(n^2)	O(n^2)
Perfect Squares	Swift	Medium	O(n^2)	O(n)
House Robber	Swift	Easy	O(n)	O(1)
House Robber II	Swift	Medium	O(n)	O(1)
Paint Fence	Swift	Easy	O(n)	O(n)
Maximum Subarray	Swift	Medium	O(n)	O(1)
Maximum Product Subarray	Swift	Medium	O(n)	O(1)
Maximum Number of Points with Cost	Swift	Medium	O(mn)	O(1)
Maximal Square	Swift	Medium	O(mn)	O(mn)
Edit Distance	Swift	Hard	O(mn)	O(mn)
Combination Sum IV	Swift	Medium	O(2^n)	O(n)
Triangle	Swift	Medium	O(2^n)	O(m)
Wiggle Subsequence	Swift	Medium	O(n)	O(1)
Wildcard Matching	Swift	Hard	O(mn)	O(mn)
Regular Expression Matching	Swift	Hard	O(mn)	O(mn)
Minimum Window Subsequence	Swift	Hard	O(mn)	O(mn)
Guess Number Higher or Lower II	Swift	Medium	O(nlogn)	O(n^2)
Burst Ballons	Swift	Hard	O(n^3)	O(n)
Frog Jump	Swift	Hard	O(n^2)	O(n)
Jump Game	Swift	Medium	O(n)	O(1)
Dungeon Game	Swift	Hard	O(nm)	O(nm)

Depth-first search

Title	Solution	Difficulty	Time	Space
Permutations	Swift	Medium	O(2^n)	O(n)
Permutations II	Swift	Medium	O(2^n)	O(n)
Subsets	Swift	Medium	O(n^n)	O(n)
Subsets II	Swift	Medium	O(2^n)	O(n)
Combinations	Swift	Medium	O(2^n)	O(n)
Combination Sum	Swift	Medium	O(2^n)	O(n)
Combination Sum II	Swift	Medium	O(2^n)	O(n)
Combination Sum III	Swift	Medium	O(2^n)	O(n)
Letter Combinations of a Phone Number	Swift	Medium	O(4^n)	O(n)
Factor Combinations	Swift	Medium	O(n^n))	O(2^n - 1)
Strobogrammatic Number II	Swift	Medium	O(m^n)	O(n)
Generalized Abbreviation	Swift	Medium	O(n^n)	O(2^n)
Palindrome Partitioning	Swift	Medium	O(n^n)	O(n)
Is Graph Bipartite	Swift	Medium	O(n)	O(n)
Number of Islands	Swift	Medium	O((mn)^2)	O(1)
Walls and Gates	Swift	Medium	O(n^n)	O(2^n)
Word Search	Swift	Medium	O((mn * 4 ^ (k - 1))	O(mn)
Word Search II	Swift	Hard	O(((mn)^2))	O(n^2)
Add and Search Word - Data structure design	Swift	Medium	O(n)	O(n)
Partition to K Equal Sum Subsets	Swift	Medium	O(k^n)	O(n)
N-Queens	Swift	Hard	O((n^n))	O(n^2)
N-Queens II	Swift	Hard	O((n^n))	O(n)
Word Squares	Swift	Hard	O((n^2))	O(n^2)
Word Pattern II	Swift	Hard	O(n^n)	O(n)
Sudoku Solver	Swift	Hard	O(n^4)	O(1)
Remove Invalid Parentheses	Swift	Hard	O(n^n)	O(n)
Expression Add Operators	Swift	Hard	O(n^n)	O(n)

Breadth-first search

Title	Solution	Difficulty	Time	Space
Word Ladder	Swift	Medium	O(nm)	O(nm)
Evaluate Division	Swift	Medium	O(n^2)	O(n)
Shortest Distance from All Buildings	Swift	Hard	O((mn)^2)	O(mn)

Math

Title	Solution	Difficulty	Time	Space
Add Binary	Swift	Easy	O(n)	O(n)
Add Two Numbers	Swift	Medium	O(n)	O(1)
Add Digits	Swift	Easy	O(1)	O(1)
Plus One	Swift	Easy	O(n)	O(1)
Missing Number	Swift	Easy	O(n)	O(1)
Divide Two Integers	Swift	Medium	O(logn)	O(1)
Number Complement	Swift	Easy	O(n)	O(1)
Hamming Distance	Swift	Easy	O(n)	O(1)
Integer Break	Swift	Medium	O(logn)	O(1)
Factorial Trailing Zeroes	Swift	Medium	O(logn)	O(1)
Happy Number	Swift	Easy	O(n)	O(n)
Single Number	Swift	Medium	O(n)	O(1)
Ugly Number	Swift	Easy	O(logn)	O(1)
Ugly Number II	Swift	Medium	O(n)	O(n)
Super Ugly Number	Swift	Medium	O(n^2)	O(n)
Count Primes	Swift	Easy	O(n)	O(n)
String to Integer (atoi)	Swift	Easy	O(n)	O(1)
Fraction to Recurring Decimal	Swift	Medium	O(logn)	O(n)
Pow(x, n)	Swift	Medium	O(logn)	O(1)
Power of Two	Swift	Easy	O(1)	O(1)
Power of Three	Swift	Easy	O(1)	O(1)
Super Power	Swift	Medium	O(n)	O(1)
Sum of Two Integers	Swift	Easy	O(n)	O(1)
Reverse Integer	Swift	Easy	O(n)	O(1)
Excel Sheet Column Number	Swift	Easy	O(n)	O(1)
Integer to Roman	Swift	Medium	O(n)	O(1)
Roman to Integer	Swift	Easy	O(n)	O(n)
Integer to English Words	Swift	Hard	O(n)	O(1)
Sparse Matrix Multiplication	Swift	Medium	O(n^3)	O(n^2)
Rectangle Area	Swift	Easy	O(1)	O(1)
Minimum Moves to Equal Array Elements	Swift	Easy	O(n)	O(1)
Pour Water	Swift	Hard	O(n)	O(n)
Trapping Rain Water	Swift	Medium	O(nk)	O(1)
Container With Most Water	Swift	Medium	O(n)	O(1)
Counting Bits	Swift	Medium	O(n)	O(n)
K-th Smallest in Lexicographical Order	Swift	Hard	O(n)	O(1)
Gary Code	Swift	Medium	O(n)	O(2^n)
Permutation Sequence	Swift	Medium	O(n^2)	O(1)
Line Reflection	Swift	Medium	O(n)	O(n)
Valid Number	Swift	Hard	O(n)	O(1)

Search

Title	Solution	Difficulty	Time	Space
Closest Binary Search Tree Value	Swift	Easy	O(logn)	O(1)
Closest Binary Search Tree Value II	Swift	Hard	O(n)	O(n)
Search in Rotated Sorted Array	Swift	Hard	O(logn)	O(1)
Search in Rotated Sorted Array II	Swift	Medium	O(logn)	O(1)
Find Minimum in Rotated Sorted Array	Swift	Medium	O(logn)	O(1)
Find Minimum in Rotated Sorted Array II	Swift	Hard	O(logn)	O(1)
Search a 2D Matrix	Swift	Medium	O(log(m + n))	O(1)
Search a 2D Matrix II	Swift	Medium	O(m + n)	O(1)
Search for a Range	Swift	Medium	O(logn)	O(1)
Search Insert Position	Swift	Medium	O(logn)	O(1)
Peak Index in a Mountain Array	Swift	Easy	O(logn)	O(1)
Find Peak Element	Swift	Medium	O(logn)	O(1)
Random Pick with Weight	Swift	Medium	O(logn)	O(1)
Sqrt(x)	Swift	Medium	O(logn)	O(1)
Median of Two Sorted Arrays	Swift	Hard	O(log(m + n))	O(1)
Minimize Max Distance to Gas Station	Swift	Hard	O(nlogm)	O(1)

Sort

Title	Solution	Difficulty	Time	Space
Merge Sorted Array	Swift	Easy	O(n)	O(1)
Sort Colors	Swift	Medium	O(n)	O(1)
Wiggle Sort	Swift	Medium	O(n)	O(1)
Wiggle Sort II	Swift	Medium	O(nlogn)	O(n)
Sort Transformed Array	Swift	Medium	O(n)	O(1)
Top K Frequent Elements	Swift	Medium	O(nlogn)	O(n)
Meeting Rooms	Swift	Easy	O(nlogn)	O(1)
Meeting Rooms II	Swift	Medium	O(nlogn)	O(n)
Merge Intervals	Swift	Hard	O(nlogn)	O(n)
Alien Dictionary	Swift	Hard	O(nm)	O(nm)
Kth Largest Element in an Array	Swift	Medium	O(nlogn)	O(n)
Array Partition I	Swift	Easy	O(nlogn)	O(n)
Insert Interval	Swift	Hard	O(n)	O(1)
Largest Number	Swift	Medium	O(nlogn)	O(1)

Graph

Title	Solution	Difficulty	Time	Space
Number of Connected Components in an Undirected Graph	Swift	Medium	O(nlogn)	O(n)
Graph Valid Tree	Swift	Medium	O(nlogn)	O(n)
Number of Islands II	Swift	Hard	O(klogmn)	O(mn)
Course Schedule	Swift	Medium	O(n)	O(n)
Course Schedule II	Swift	Medium	O(n)	O(n)

Design

Title	Solution	Difficulty	Time	Space
Shuffle an Array	Swift	Easy	O(n)	O(1)
Design HashMap	Swift	Easy	O(n)	O(n)
Design Tic-Tac-Toe	Swift	Medium	O(1)	O(n)
Flatten Nested List Iterator	Swift	Medium	O(n)	O(n)
Flatten 2D Vector	Swift	Medium	O(n)	O(n)
Implement Trie (Prefix Tree)	Swift	Medium	O(n)	O(n)
Add and Search Word - Data structure design	Swift	Medium	O(24^n)	O(n)
Insert Delete GetRandom O(1)	Swift	Medium	O(1)	O(n)
LRU Cache	Swift	Hard	O(1)	O(n)
All O`one Data Structure	Swift	Hard	O(1)	O(n)

Google

Title	Solution	Difficulty	Frequency
Race Car	Swift	Hard	★★★★★★
Plus One	Swift	Easy	★★★★★★
Number of Islands	Swift	Medium	★★★★
Summary Ranges	Swift	Medium	★★★★
Perfect Squares	Swift	Medium	★★★★
Merge Intervals	Swift	Hard	★★★
Valid Parentheses	Swift	Easy	★★★
Trapping Rain Water	Swift	Hard	★★
Merge k Sorted Lists	Swift	Hard	★★
Longest Consecutive Sequence	Swift	Hard	★★
Find Peak Element	Swift	Medium	★★
Power of Two	Swift	Easy	★★
Spiral Matrix	Swift	Medium	★★
Sliding Window Maximum	Swift	Hard	★★
Pow(x, n)	Swift	Medium	★★
Letter Combinations of a Phone Number	Swift	Medium	★★
Heaters	Swift	Easy	★

Facebook

Title	Solution	Difficulty	Frequency
3Sum	Swift	Medium	★★★★★★
Valid Palindrome	Swift	Easy	★★★★★★
Valid Palindrome II	Swift	Easy	★★★★★★
Move Zeroes	Swift	Easy	★★★★★★
Remove Invalid Parentheses	Swift	Hard	★★★★★★
Add Binary	Swift	Easy	★★★★★
Two Sum	Swift	Easy	★★★★★
Binary Tree Paths	Swift	Easy	★★★★
Letter Combinations of a Phone Number	Swift	Medium	★★★★
Merge k Sorted Lists	Swift	Hard	★★★★
Reverse Linked List	Swift	Easy	★★★
Merge Intervals	Swift	Hard	★★★
Number of Islands	Swift	Medium	★★★
Reverse Linked List	Swift	Easy	★★★
Expression Add Operators	Swift	Hard	★★★
Subsets	Swift	Medium	★★★
Sort Colors	Swift	Medium	★★

Snapchat

Title	Solution	Difficulty	Frequency
Game of Life	Swift	Medium	★★★★★★
Meeting Rooms II	Swift	Medium	★★★★★★
Valid Sudoku	Swift	Easy	★★★★★
Binary Tree Vertical Order Traversal	Swift	Medium	★★★★
Alien Dictionary	Swift	Hard	★★★★
One Edit Distance	Swift	Medium	★★★
Sudoku Solver	Swift	Hard	★★★
Reverse Linked List	Swift	Easy	★★
Unique Binary Search Trees	Swift	Medium	★★
Minimum Window Substring	Swift	Hard	★★
Remove K Digits	Swift	Medium	★
Ternary Expression Parser	Swift	Medium	★

Uber

Title	Solution	Difficulty	Frequency
Valid Sudoku	Swift	Easy	★★★★
Spiral Matrix	Swift	Medium	★★★★
Letter Combinations of a Phone Number	Swift	Medium	★★★★
Group Anagrams	Swift	Medium	★★★★
Word Pattern	Swift	Easy	★★★
Roman to Integer	Swift	Easy	★★★
Combination Sum	Swift	Medium	★★

Airbnb

Title	Solution	Difficulty	Frequency
Two Sum	Swift	Easy	★★★★★
Text Justification	Swift	Hard	★★★★
House Robber	Swift	Easy	★★
Single Number	Swift	Medium	★★
Word Search II	Swift	Hard	★★
Add Two Numbers	Swift	Medium	★★

LinkedIn

Title	Solution	Difficulty	Frequency
Maximum Subarray	Swift	Medium	★★★★★★
Pow(x, n)	Swift	Medium	★★★★★★
Merge Intervals	Swift	Hard	★★★★★★
Isomorphic Strings	Swift	Easy	★★★★★★
Search in Rotated Sorted Array	Swift	Hard	★★★★★
Search for a Range	Swift	Medium	★★★★★
Two Sum	Swift	Easy	★★★★
Binary Tree Level Order Traversal	Swift	Easy	★★★★
Evaluate Reverse Polish Notation	Swift	Medium	★★★
Maximum Product Subarray	Swift	Medium	★★★
Product of Array Except Self	Swift	Medium	★★★
Symmetric Tree	Swift	Easy	★★

Amazon

Title	Solution	Difficulty	Frequency
Two Sum	Swift	Easy	★★★★★★
Min Cost Climbing Stairs	Swift	Easy	★★★★
Number of Islands	Swift	Medium	★★
Add Two Numbers	Swift	Medium	★★
Reverse Linked List	Swift	Easy	★★
Valid Parentheses	Swift	Easy	★★
Longest Palindromic Substring	Swift	Medium	★★
Trapping Rain Water	Swift	Hard	★★
Longest Substring Without Repeating Characters	Swift	Medium	★★
Letter Combinations of a Phone Number	Swift	Medium	★★
Valid Anagram	Swift	Easy	★★
Rotate Image	Swift	Medium	★★
Best Time to Buy and Sell Stock	Swift	Easy	★★
3Sum	Swift	Medium	★★
Sliding Window Maximum	Swift	Hard	★★

Microsoft

Title	Solution	Difficulty	Frequency
Reverse Linked List	Swift	Easy	★★★★★★
Two Sum	Swift	Easy	★★★★★
String to Integer (atoi)	Swift	Easy	★★★★
Add Two Numbers	Swift	Medium	★★★★
Excel Sheet Column Number	Swift	Easy	★★★★
Validate Binary Search Tree	Swift	Medium	★★★
Merge Two Sorted Lists	Swift	Easy	★★★

Problem Status

Solution	Number	Title	Difficulty
Swift	460	LFU Cache	Hard
Swift	448	Find All Numbers Disappeared in an Array	Easy
Swift	377	Combination Sum IV	Medium
	376	Wiggle Subsequence	Medium
Swift	375	Guess Number Higher or Lower II	Medium
	374	Guess Number Higher or Lower	Easy
	373	Find K Pairs with Smallest Sums	Medium
Swift	372	Super Pow	Medium
Swift	371	Sum of Two Integers	Easy
	370	Range Addition ♥	Medium
	369	Plus One Linked List ♥	Medium
	368	Largest Divisible Subset	Medium
	367	Valid Perfect Square	Medium
	366	Find Leaves of Binary Tree ♥	Medium
	365	Water and Jug Problem	Medium
Swift	364	Nested List Weight Sum II ♥	Medium
	363	Max Sum of Rectangle No Larger Than K	Hard
	362	Design Hit Counter ♥	Medium
	361	Bomb Enemy ♥	Medium
Swift	360	Sort Transformed Array ♥	Medium
	359	Logger Rate Limiter ♥	Easy
	358	Rearrange String k Distance Apart ♥	Hard
	357	Count Numbers with Unique Digits	Medium
	356	Line Reflection ♥	Medium
	355	Design Twitter	Medium
	354	Russian Doll Envelopes	Hard
	353	Design Snake Game ♥	Medium
	352	Data Stream as Disjoint Intervals	Hard
	351	Android Unlock Patterns ♥	Medium
Swift	350	Intersection of Two Arrays II	Easy
Swift	349	Intersection of Two Arrays	Easy
	348	Design Tic-Tac-Toe ♥	Medium
Swift	347	Top K Frequent Elements	Medium
	346	Moving Average from Data Stream ♥	Easy
Swift	345	Reverse Vowels of a String	Easy
Swift	344	Reverse String	Easy
Swift	343	Integer Break	Medium
	342	Power of Four	Easy
Swift	341	Flatten Nested List Iterator	Medium
Swift	340	Longest Substring with At Most K Distinct Characters ♥	Hard
Swift	339	Nested List Weight Sum ♥	Easy
Swift	338	Counting Bits	Medium
Swift	337	House Robber III	Medium
	336	Palindrome Pairs	Hard
	335	Self Crossing	Hard
Swift	334	Increasing Triplet Subsequence	Medium
	333	Largest BST Subtree ♥	Medium
	332	Reconstruct Itinerary	Medium
	331	Verify Preorder Serialization of a Binary Tree	Medium
	330	Patching Array	Hard
	329	Longest Increasing Path in a Matrix	Hard
Swift	328	Odd Even Linked List	Medium
	327	Count of Range Sum	Hard
Swift	326	Power of Three	Easy
Swift	325	Maximum Size Subarray Sum Equals k ♥	Medium
Swift	324	Wiggle Sort II	Medium
Swift	323	Number of Connected Components in an Undirected Graph ♥	Medium
Swift	322	Coin Change	Medium
Swift	321	Create Maximum Number	Hard
Swift	320	Generalized Abbreviation ♥	Medium
	319	Bulb Switcher	Medium
	318	Maximum Product of Word Lengths	Medium
Swift	317	Shortest Distance from All Buildings ♥	Hard
	316	Remove Duplicate Letters	Hard
	315	Count of Smaller Numbers After Self	Hard
Swift	314	Binary Tree Vertical Order Traversal ♥	Medium
Swift	313	Super Ugly Number	Medium
Swift	312	Burst Balloons	Hard
Swift	311	Sparse Matrix Multiplication ♥	Medium
	310	Minimum Height Trees	Medium
Swift	309	Best Time to Buy and Sell Stock with Cooldown	Medium
	308	Range Sum Query 2D - Mutable ♥	Hard
	307	Range Sum Query - Mutable	Medium
	306	Additive Number	Medium
Swift	305	Number of Islands II ♥	Hard
Swift	304	Range Sum Query 2D - Immutable	Medium
	303	Range Sum Query - Immutable	Easy
	302	Smallest Rectangle Enclosing Black Pixels ♥	Hard
Swift	301	Remove Invalid Parentheses	Hard
Swift	300	Longest Increasing Subsequence	Medium
	299	Bulls and Cows	Easy
	298	Binary Tree Longest Consecutive Sequence ♥	Medium
	297	Serialize and Deserialize Binary Tree	Hard
Swift	296	Best Meeting Point ♥	Hard
	295	Find Median from Data Stream	Hard
Swift	294	Flip Game II ♥	Medium
Swift	293	Flip Game ♥	Easy
	292	Nim Game	Easy
	291	Word Pattern II ♥	Hard
Swift	290	Word Pattern	Easy
Swift	289	Game of Life	Medium
	288	Unique Word Abbreviation ♥	Easy
	287	Find the Duplicate Number	Hard
Swift	286	Walls and Gates ♥	Medium
	285	Inorder Successor in BST ♥	Medium
	284	Peeking Iterator	Medium
Swift	283	Move Zeroes	Easy
Swift	282	Expression Add Operators	Hard
	281	Zigzag Iterator ♥	Medium
Swift	280	Wiggle Sort ♥	Medium
Swift	279	Perfect Squares	Medium
	278	First Bad Version	Easy
	277	Find the Celebrity ♥	Medium
Swift	276	Paint Fence ♥	Easy
	275	H-Index II	Medium
	274	H-Index	Medium
Swift	273	Integer to English Words	Hard
Swift	272	Closest Binary Search Tree Value II ♥	Hard
	271	Encode and Decode Strings ♥	Medium
Swift	270	Closest Binary Search Tree Value ♥	Easy
Swift	269	Alien Dictionary ♥	Hard
Swift	268	Missing Number	Easy
	267	Palindrome Permutation II ♥	Medium
Swift	266	Palindrome Permutation ♥	Easy
Swift	265	Paint House II ♥	Hard
Swift	264	Ugly Number II	Medium
Swift	263	Ugly Number	Easy
Swift	261	Graph Valid Tree ♥	Medium
	260	Single Number III	Medium
	259	3Sum Smaller ♥	Medium
Swift	258	Add Digits	Easy
Swift	257	Binary Tree Paths	Easy
Swift	256	Paint House ♥	Medium
	255	Verify Preorder Sequence in Binary Search Tree ♥	Medium
Swift	254	Factor Combinations ♥	Medium
Swift	253	Meeting Rooms II ♥	Medium
Swift	252	Meeting Rooms ♥	Easy
Swift	251	Flatten 2D Vector ♥	Medium
	250	Count Univalue Subtrees ♥	Medium
	249	Group Shifted Strings ♥	Easy
	248	Strobogrammatic Number III ♥	Hard
Swift	247	Strobogrammatic Number II ♥	Medium
Swift	246	Strobogrammatic Number ♥	Easy
Swift	245	Shortest Word Distance III ♥	Medium
Swift	244	Shortest Word Distance II ♥	Medium
Swift	243	Shortest Word Distance ♥	Easy
Swift	242	Valid Anagram	Easy
Swift	241	Different Ways to Add Parentheses	Medium
Swift	240	Search a 2D Matrix II	Medium
Swift	239	Sliding Window Maximum	Hard
Swift	238	Product of Array Except Self	Medium
	237	Delete Node in a Linked List	Easy
	236	Lowest Common Ancestor of a Binary Tree	Medium
Swift	235	Lowest Common Ancestor of a Binary Search Tree	Easy
Swift	234	Palindrome Linked List	Easy
	233	Number of Digit One	Hard
Swift	232	Implement Queue using Stacks	Easy
Swift	231	Power of Two	Easy
Swift	230	Kth Smallest Element in a BST	Medium
Swift	229	Majority Element II	Medium
Swift	228	Summary Ranges	Medium
	227	Basic Calculator II	Medium
Swift	226	Invert Binary Tree	Easy
	225	Implement Stack using Queues	Easy
Swift	224	Basic Calculator	Hard
Swift	223	Rectangle Area	Easy
	222	Count Complete Tree Nodes	Medium
Swift	221	Maximal Square	Medium
	220	Contains Duplicate III	Medium
Swift	219	Contains Duplicate II	Easy
	218	The Skyline Problem	Hard
Swift	217	Contains Duplicate	Easy
Swift	216	Combination Sum III	Medium
Swift	215	Kth Largest Element in an Array	Medium
	214	Shortest Palindrome	Hard
Swift	213	House Robber II	Medium
Swift	212	Word Search II	Hard
Swift	211	Add and Search Word - Data structure design	Medium
Swift	210	Course Schedule II	Medium
Swift	209	Minimum Size Subarray Sum	Medium
Swift	208	Implement Trie (Prefix Tree)	Medium
Swift	207	Course Schedule	Medium
Swift	206	Reverse Linked List	Easy
Swift	205	Isomorphic Strings	Easy
Swift	204	Count Primes	Easy
Swift	203	Remove Linked List Elements	Easy
Swift	202	Happy Number	Easy
	201	Bitwise AND of Numbers Range	Medium
Swift	200	Number of Islands	Medium
Swift	199	Binary Tree Right Side View	Medium
Swift	198	House Robber	Easy
	191	Number of 1 Bits	Easy
	190	Reverse Bits	Easy
Swift	189	Rotate Array	Easy
Swift	188	Best Time to Buy and Sell Stock IV	Hard
	187	Repeated DNA Sequences	Medium
Swift	186	Reverse Words in a String II ♥	Medium
Swift	179	Largest Number	Medium
	174	Dungeon Game	Hard
Swift	173	Binary Search Tree Iterator	Medium
Swift	172	Factorial Trailing Zeroes	Easy
Swift	171	Excel Sheet Column Number	Easy
Swift	170	Two Sum III - Data structure design ♥	Easy
Swift	169	Majority Element	Easy
	168	Excel Sheet Column Title	Easy
Swift	167	Two Sum II - Input array is sorted ♥	Medium
Swift	166	Fraction to Recurring Decimal	Medium
	165	Compare Version Numbers	Easy
	164	Maximum Gap	Hard
Swift	163	Missing Ranges ♥	Medium
Swift	162	Find Peak Element	Medium
Swift	161	One Edit Distance♥	Medium
	160	Intersection of Two Linked Lists	Easy
Swift	159	Longest Substring with At Most Two Distinct Characters ♥	Hard
	158	Read N Characters Given Read4 II - Call multiple times ♥	Hard
	157	Read N Characters Given Read4 ♥	Easy
Swift	156	Binary Tree Upside Down ♥	Medium
Swift	155	Min Stack	Easy
Swift	154	Find Minimum in Rotated Sorted Array II	Hard
Swift	153	Find Minimum in Rotated Sorted Array	Medium
Swift	152	Maximum Product Subarray	Medium
Swift	151	Reverse Words in a String	Medium
Swift	150	Evaluate Reverse Polish Notation	Medium
	149	Max Points on a Line	Hard
	148	Sort List	Medium
	147	Insertion Sort List	Medium
Swift	146	LRU Cache	Hard
Swift	145	Binary Tree Postorder Traversal	Hard
Swift	144	Binary Tree Preorder Traversal	Medium
Swift	143	Reorder List	Medium
	142	Linked List Cycle II	Medium
	141	Linked List Cycle	Easy
	140	Word Break II	Hard
	139	Word Break	Medium
	138	Copy List with Random Pointer	Hard
Swift	137	Single Number II	Medium
Swift	136	Single Number	Medium
	135	Candy	Hard
Swift	134	Gas Station	Medium
	133	Clone Graph	Medium
	132	Palindrome Partitioning II	Hard
Swift	131	Palindrome Partitioning	Medium
	130	Surrounded Regions	Medium
	129	Sum Root to Leaf Numbers	Medium
Swift	128	Longest Consecutive Sequence	Hard
Swift	127	Word Ladder	Medium
	126	Word Ladder II	Hard
Swift	125	Valid Palindrome	Easy
Swift	124	Binary Tree Maximum Path Sum	Hard
Swift	123	Best Time to Buy and Sell Stock III	Hard
Swift	122	Best Time to Buy and Sell Stock II	Medium
Swift	121	Best Time to Buy and Sell Stock	Easy
Swift	120	Triangle	Medium
	119	Pascal’s Triangle II	Easy
	118	Pascal’s Triangle	Easy
	117	Populating Next Right Pointers in Each Node II	Hard
	116	Populating Next Right Pointers in Each Node	Medium
	115	Distinct Subsequences	Hard
Swift	114	Flatten Binary Tree to Linked List	Medium
Swift	113	Path Sum II	Medium
Swift	112	Path Sum	Easy
Swift	111	Minimum Depth of Binary Tree	Easy
Swift	110	Balanced Binary Tree	Easy
	109	Convert Sorted List to Binary Search Tree	Medium
Swift	108	Convert Sorted Array to Binary Search Tree	Medium
Swift	107	Binary Tree Level Order Traversal II	Easy
Swift	106	Construct Binary Tree from Inorder and Postorder Traversal	Medium
Swift	105	Construct Binary Tree from Preorder and Inorder Traversal	Medium
Swift	104	Maximum Depth of Binary Tree	Easy
Swift	103	Binary Tree Zigzag Level Order Traversal	Medium
Swift	102	Binary Tree Level Order Traversal	Easy
Swift	101	Symmetric Tree	Easy
Swift	100	Same Tree	Easy
Swift	99	Recover Binary Search Tree	Hard
Swift	98	Validate Binary Search Tree	Medium
	97	Interleaving String	Hard
Swift	96	Unique Binary Search Trees	Medium
	95	Unique Binary Search Trees II	Medium
Swift	94	Binary Tree Inorder Traversal	Medium
	93	Restore IP Addresses	Medium
	92	Reverse Linked List II	Medium
Swift	91	Decode Ways	Medium
Swift	90	Subsets II	Medium
Swift	89	Gray Code	Medium
Swift	88	Merge Sorted Array	Easy
	87	Scramble String	Hard
Swift	86	Partition List	Medium
	85	Maximal Rectangle	Hard
	84	Largest Rectangle in Histogram	Hard
Swift	83	Remove Duplicates from Sorted List	Easy
Swift	82	Remove Duplicates from Sorted List II	Medium
Swift	81	Search in Rotated Sorted Array II	Medium
Swift	80	Remove Duplicates from Sorted Array II	Medium
Swift	79	Word Search	Medium
Swfit	78	Subsets	Medium
Swift	77	Combinations	Medium
Swift	76	Minimum Window Substring	Hard
Swift	75	Sort Colors	Medium
Swift	74	Search a 2D Matrix	Medium
Swift	73	Set Matrix Zeroes	Medium
Swift	72	Edit Distance	Hard
Swift	71	Simplify Path	Medium
Swift	70	Climbing Stairs	Easy
Swift	69	Sqrt(x)	Medium
Swift	68	Text Justification	Hard
Swift	67	Add Binary	Easy
Swift	66	Plus One	Easy
Swift	65	Valid Number	Hard
Swift	64	Minimum Path Sum	Medium
Swift	63	Unique Paths II	Medium
Swift	62	Unique Paths	Medium
Swift	61	Rotate List	Medium
Swift	60	Permutation Sequence	Medium
Swift	59	Spiral Matrix II	Medium
Swift	58	Length of Last Word	Easy
Swift	57	Insert Interval	Hard
Swift	56	Merge Intervals	Hard
Swift	55	Jump Game	Medium
Swift	54	Spiral Matrix	Medium
Swift	53	Maximum Subarray	Medium
Swift	52	N-Queens II	Hard
Swift	51	N-Queens	Hard
Swift	50	“Pow(x, n)”	Medium
Swift	49	Group Anagrams	Medium
Swift	48	Rotate Image	Medium
Swift	47	Permutations II	Medium
Swift	46	Permutations	Medium
	45	Jump Game II	Hard
Swift	44	Wildcard Matching	Hard
Swift	43	Multiply Strings	Medium
Swift	42	Trapping Rain Water	Hard
Swift	41	First Missing Positive	Hard
Swift	40	Combination Sum II	Medium
Swift	39	Combination Sum	Medium
Swift	38	Count and Say	Easy
Swift	37	Sudoku Solver	Hard
Swift	36	Valid Sudoku	Easy
Swift	35	Search Insert Position	Medium
Swift	34	Search for a Range	Medium
Swift	33	Search in Rotated Sorted Array	Hard
Swift	32	Longest Valid Parentheses	Hard
Swift	31	Next Permutation	Medium
	30	Substring with Concatenation of All Words	Hard
Swift	29	Divide Two Integers	Medium
Swift	28	Implement strStr()	Easy
Swfit	27	Remove Element	Easy
Swift	26	Remove Duplicates from Sorted Array	Easy
Swift	25	Reverse Nodes in k-Group	Hard
Swift	24	Swap Nodes in Pairs	Easy
Swift	23	Merge k Sorted Lists	Hard
Swift	22	Generate Parentheses	Medium
Swift	21	Merge Two Sorted Lists	Easy
Swift	20	Valid Parentheses	Easy
Swift	19	Remove Nth Node From End of List	Easy
Swift	18	4Sum	Medium
Swift	17	Letter Combinations of a Phone Number	Medium
Swift	16	3Sum Closest	Medium
Swift	15	3Sum	Medium
Swift	14	Longest Common Prefix	Easy
Swift	13	Roman to Integer	Easy
Swift	12	Integer to Roman	Medium
Swift	11	Container With Most Water	Medium
Swift	10	Regular Expression Matching	Hard
Swift	9	Palindrome Number	Easy
Swift	8	String to Integer (atoi)	Easy
Swift	7	Reverse Integer	Easy
Swift	6	ZigZag Conversion	Easy
Swift	5	Longest Palindromic Substring	Medium
Swift	4	Median of Two Sorted Arrays	Hard
Swift	3	Longest Substring Without Repeating Characters	Medium
Swift	2	Add Two Numbers	Medium
Swift	1	Two Sum	Easy