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Swift

682 problems50 sections📅 2026 curriculum

Learn Swift by typing safe, idiomatic code.

Type your way through Swift: optionals and optional binding, closures, protocols and protocol extensions, enums with associated values, and value-type structs. Every snippet is idiomatic Swift, and an AI tutor explains each line — how optional chaining stays safe, why protocol-oriented design beats subclassing — so the language's safety model sticks while you build speed.

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Run Swift on your machine

1. Install the toolchain

xcode-select --install # macOS, or see swift.org

2. Save your code as hello.swift, then compile & run

swift hello.swift

Official install docs ↗

progress by section

1Fundamentals0/8start →

Hello, Swift let vs var if and the ternary Type annotations Functions for and while switch guard for early exit

2Strings In Depth0/18start →

Length and emptiness Change case String and Character Concatenate Interpolation Iterate characters Search a string Join a sequence Multiline literals Parse and format numbers Replace text Reverse a string Split into pieces Trim whitespace Substring String indices Offset an index Unicode scalars

3Values & References0/16start →

Classes share on assign Structs copy on assign Value vs reference types Arrays are value types A class arg is shared Enums are value types Identity with ===inout parameters Swap with inout let makes a struct constant A struct arg is a copy let on a class binds the reference Mutating methods ARC and deinit Shared ownership weak breaks a cycle

4Slices & Arrays0/17Unlock →

Arrays Closed range contains and firstIndex dropFirst and dropLast first and last min, max, reduce Partial ranges prefix and suffix Slice a half-open range Reverse order sort mutates in place sorted returns a copy filter and map indices and enumerated prefix(while:)Custom order ArraySlice keeps indices

5Data structures0/9Unlock →

Array basics Set dedup Tuples Dictionary word count Array as a queue Array as a stack Structs Nested collections A generic stack

6Iterators0/20Unlock →

7Traits0/20Unlock →

8Generics0/20Unlock →

9Lifetimes0/20Unlock →

10Closures0/20Unlock →

11Pattern Matching0/20Unlock →

12Error Handling0/20Unlock →

13Option & Result0/20Unlock →

14Conversions0/15Unlock →

Value to String Bool as a number Character and Unicode scalar Characters to String Int from a String Numeric conversion via initializers Slice to Array String to [Character]Float to Int truncates Build a typed collection Data and String Flexible generic parameter Parse with a radix Format with a radix LosslessStringConvertible

15Collection Conversions0/19Unlock →

Array to Set Flatten nested Arrays Dictionary keys to Array Pairs to a Dictionary Set to sorted Array Unique and sorted at once Dictionary values to Array Dictionary to pairs Frequency map Keys to a Set mapValues Set operations Iterate keys in order Two Arrays to a Dictionary Array and ContiguousArray Group into a Dictionary Invert a Dictionary Unique, keeping order An Array of a protocol type

16Math0/14Unlock →

Math constants Float functions Integer arithmetic min, max, clamp Rounding Factorial Logarithms & exp Trigonometry Greatest common divisor hypot & atan2 Primality test Float modulo & signum Integer overflow Mean, median, stdev

17Encoding0/22Unlock →

18Random0/20Unlock →

19Data I/O0/18Unlock →

Parse CSV into rows Tab-separated values Build a CSV string Select one column CSV into a number matrix Split off the header Whitespace-separated matrix Serialize records to CSV Skip blanks and comments Print an aligned table Write CSV to a file Write a matrix as text Decode JSON to Codable Encode Codable to JSON Parse untyped JSON Parse key=value config Round-trip write then read Drop unparseable rows

20Linear Algebra0/21Unlock →

21Text Processing0/16Unlock →

Word count Count occurrences Strip all whitespace Replace text Reverse word order Title case Count vowels Zero-pad a number Pad and align Capitalize the first letter Character frequency Index each character Longest word Number the lines Truncate with an ellipsis Levenshtein distance

22Date & Time0/12Unlock →

Now and the epoch Timestamp round-trip Add to a date Read date components Build a date from components Difference between dates Custom date format Seconds to HH:MM:SS ISO 8601 format Weekday Leap year check Parse a clock string

23Memory0/12Unlock →

Swap in place Value vs reference Arrays are copy-on-write Reference identity MemoryLayout size MemoryLayout alignment ARC lifecycle MemoryLayout stride Unowned reference Weak reference Copy-on-write withUnsafeBytes

24Modules0/20Unlock →

25Macros0/20Unlock →

26Testing0/20Unlock →

27Algorithms0/8Unlock →

Greatest common divisor Reverse a string Binary search Palindrome check Fibonacci with memoization Merge two sorted arrays Two sum Quicksort

28Sorting Algorithms0/12Unlock →

Check if sorted Standard library sorts Bubble sort Sort by key and descending Insertion sort Selection sort Counting sort Merge sort Shell sort Heapsort Quicksort (in place)Radix sort

29Expression Parsing0/6Unlock →

Evaluate postfix (RPN)Tokenize an expression Evaluate infix Recursive-descent calculator Right-associative power Shunting-yard

30Idioms0/9Unlock →

guard for early exit map / filter / reduce chain Trailing closures defer Enum with associated values Optional chaining Key paths Protocol extension Result builder

31OOP & Traits0/8Unlock →

Value vs reference type Access control & static Computed & observed properties Enum with data & methods Inheritance & override init and deinit Lazy stored property Protocol-oriented composition

32Trait Objects0/14Unlock →

Array of a protocol type Default method via any Take an any Protocol Return any Protocol Filter [Any] by type Class-constrained protocol is / as? casts Array of closures Inherited protocol existential Opaque return type Reduce over any Protocol some vs any A factory registry Type erasure (AnyShape)

33Design Patterns0/14Unlock →

Prototype Factory Method Singleton Adapter Builder Lazy Initialization Observer Strategy Command Decorator Dependency Injection Object Pool State Actor

34Async0/3Unlock →

async func and await Concurrent work with async let AsyncStream and continuations

35File I/O0/6Unlock →

Read a file Write a file Read with an encoding Read lines Temp file round-trip Append with FileHandle

36Filesystem0/18Unlock →

Does a path exist?Copy a file Create nested directories Files vs directories Build a path Rename or move List a directory Change the extension File metadata Path components Remove a file Sorted listing Write to the temp dir Absolute path Filter by extension Last modified time Total size of a tree Walk the tree

37Networking0/16Unlock →

Parse the request line Route by path Classify an IP address Parse a socket address Bind an ephemeral port Build an HTTP response Read a line from a stream Resolve a hostname Shut down a connection TCP client Read timeout UDP receive UDP send A thread per connection TCP echo server Host a web page

38Concurrency0/7Unlock →

async/await with Task Parallel results with async let Task.detached Shared state with an actor DispatchQueue and DispatchSemaphore Sendable snapshots from an actor Fan out with withTaskGroup

39Unsafe & FFI0/14Unlock →

Dereference a raw pointer A C function pointer Size, stride, and alignment Inspect a value's bytes A typed buffer pointer Call a C function C strings Raw and mutable raw pointers Mutate a value's bytes Reinterpret the bits A mutable buffer pointer Pointer arithmetic Raw bytes to typed elements Ownership through a raw pointer

40Commands0/14Unlock →

Command-line arguments Skip the program name Env var with a default Read an environment variable Current directory Iterate all env vars Set and remove a variable Path to this program Exit with a code Run a command Pass env to a child Spawn and wait Command exit status Read all of stdin

41Array0/10Unlock →

Contains Duplicate Two Sum Best Time to Buy and Sell Stock Maximum Subarray Container With Most Water Find Minimum in Rotated Sorted Array Product of Array Except Self Maximum Product Subarray Search in Rotated Sorted Array 3Sum

42Binary0/5Unlock →

Missing Number Number of 1 Bits Counting Bits Reverse Bits Sum of Two Integers

43String0/10Unlock →

Valid Anagram Valid Palindrome Valid Parentheses Encode and Decode Strings Group Anagrams Longest Substring Without Repeating Characters Longest Repeating Character Replacement Longest Palindromic Substring Palindromic Substrings Minimum Window Substring

44Matrix0/4Unlock →

Rotate Image Set Matrix Zeroes Spiral Matrix Word Search

45Interval0/5Unlock →

Meeting Rooms Merge Intervals Insert Interval Non-overlapping Intervals Meeting Rooms II

46Linked List0/6Unlock →

Reverse Linked List Linked List Cycle Merge Two Sorted Lists Remove Nth Node From End Merge K Sorted Lists Reorder List

47Tree0/14Unlock →

Maximum Depth of Binary Tree Invert Binary Tree Same Tree Lowest Common Ancestor of a BST Binary Tree Level Order Traversal Subtree of Another Tree Implement Trie (Prefix Tree)Kth Smallest Element in a BST Validate Binary Search Tree Add and Search Word Construct Binary Tree from Preorder and Inorder Binary Tree Maximum Path Sum Serialize and Deserialize Binary Tree Word Search II

48Graph0/8Unlock →

Number of Connected Components Number of Islands Clone Graph Course Schedule Longest Consecutive Sequence Graph Valid Tree Alien Dictionary Pacific Atlantic Water Flow

49Heap0/3Unlock →

Kth Largest Element in an Array Top K Frequent Elements Find Median from Data Stream

50Dynamic Programming0/11Unlock →

Climbing Stairs House Robber Unique Paths Coin Change House Robber II Jump Game Combination Sum IV Decode Ways Longest Common Subsequence Longest Increasing Subsequence Word Break