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Clojure

688 problems50 sections📅 2026 curriculum

Learn Clojure by typing real, functional Lisp.

Type your way into Clojure's Lisp syntax: persistent immutable data structures, pure higher-order functions, destructuring, and the -> and ->> threading macros that make nested calls readable. Each snippet is idiomatic Clojure, and an AI tutor explains every line — how a persistent map shares structure, why the threading macro reorders your reading — so the parentheses stop being scary.

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Run Clojure on your machine

1. Install the toolchain

brew install clojure/tools/clojure # (needs a JDK)

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

clojure -M hello.clj

Official install docs ↗

progress by section

1Fundamentals0/11start →

Hello, Clojure Arithmetic def and str Comparison defn and fn if and when Keywords let bindings cond do loop and recur

2Strings In Depth0/16start →

Build with str count starts-with? / ends-with?blank?Change case includes?trim format join split-lines replace reverse split subs Strings are seqable Thread transforms

3Values & References0/14start →

Immutability Value equality The @ reader macro Batch with into No aliasing surprises Persistent data Vars atom An atom over a collection swap! and reset!identical? vs == across seq types Structural sharing Dynamic binding

4Slices & Arrays0/15Unlock →

Head and tail reverse and rseq take and drop nth sort and sort-by subvec take-last and drop-last concat and flatten contains? caveat partition split-at take-nth take-while and drop-while partition-by Overlapping windows

5Data structures0/12Unlock →

Lists Hash maps Vectors assoc and dissoc frequencies Sets update conj is polymorphic sorted-map sorted-set Nested access defrecord

6Iterators0/21Unlock →

7Traits0/20Unlock →

8Generics0/18Unlock →

One fn, many types Generic over any seq compare Generic container Parametric via higher-order Generic minimum Generic sort by comparator Build a value generically Records are maps Static vs dynamic dispatch Extend built-in types Multimethods Newtype wrapper Protocols Runtime protocol check Ad-hoc hierarchies Dispatch on many args reify

9Lifetimes0/20Unlock →

10Closures0/20Unlock →

11Pattern Matching0/20Unlock →

12Error Handling0/21Unlock →

13Option & Result0/20Unlock →

14Conversions0/15Unlock →

str renders values Cast to double Double/parseDouble Integer/parseInt char and int chars and string format a value Cast to int name and keyword parse-double parse-long parseInt with a radix seq and vec vec and set Bit and base strings

15Collection Conversions0/19Unlock →

keys of a map Build a set sort vals of a map Build a vector distinct, keep order flatten nesting frequencies into another collection sort-by a field zipmap two seqs Set difference group-by a key Set intersection Pairs to a map Invert a map mapcat one level Into a sorted-set Set union

16Math0/14Unlock →

Math constants Float functions Integer arithmetic min, max, clamp Rounding Logarithms & exp Trigonometry Bit math Factorial Greatest common divisor hypot & atan2 quot, rem and mod Primality test Mean, median, stddev

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 Read a data file Skip blanks and comments Print an aligned table Write CSV to a file Write a matrix as text Append a row Stream lines with a reader Serialize a map to JSON Parse key=value config Round-trip write then read Drop unparseable rows

20Linear Algebra0/21Unlock →

21Text Processing0/16Unlock →

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

22Date & Time0/12Unlock →

Build a date-time Current date and time Date components Format a date-time Leap year check Add days and months Days between dates Duration to H:M:S UNIX epoch time Parse a date-time Period between dates Convert between zones

23Memory0/12Unlock →

Swap without a temp identical? vs =Immutable update atom for state memoize Structural sharing identityHashCode Interned keywords volatile!agent for async state refs and dosync Transients

24Modules0/20Unlock →

25Macros0/20Unlock →

26Testing0/20Unlock →

27Algorithms0/10Unlock →

Frequencies Palindrome (two-pointer)Greatest common divisor Binary search Fibonacci with memoization Merge sorted seqs Quicksort Two sum Linear congruential generator Fisher-Yates shuffle

28Sorting Algorithms0/12Unlock →

Built-in sort Check if sorted Bubble sort Insertion sort Selection sort Counting sort Sort by multiple keys Merge sort Quicksort Shell sort Heapsort Radix sort

29Expression Parsing0/6Unlock →

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

30Idioms0/9Unlock →

Destructuring doseq for side effects Keywords and sets as fns if-let for optionals Thread-first ->Thread-last ->>cond->update and update-in into with a transducer

31OOP & Traits0/8Unlock →

Protocol as interface defrecord with fields Composition over inheritance Shared behavior deftype Multimethod polymorphism Polymorphism via protocols A show protocol

32Trait Objects0/14Unlock →

Default behavior Return one of several types Dispatch through a protocol Two protocols on one type A vector of functions Vary the sequence type Dispatch on class reify capturing locals Freely shared values Sum across mixed types A vector of implementers Multimethod hierarchy A handler registry Recover the concrete type

33Design Patterns0/14Unlock →

defonce singleton Threaded map builder delay / force Prototype via merge Strategy as fns Protocol adapter Command closures Function decorator Injected collaborators Multimethod factory add-watch observer State transition table Agent actor Object pool atom

34Async0/6Unlock →

delay and force future and promise core.async, terminating lazy-seq as a generator Parallel map Producer / consumer

35File I/O0/6Unlock →

Does a file exist?Write and read a file Read all lines Round-trip via a temp file Append with a writer Read lines with a reader

36Filesystem0/18Unlock →

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

37Networking0/16Unlock →

An IP address The local host Parse the request line Route by path A socket address Parse a URI Parse a URL An ephemeral port Build an HTTP response Read a line from a stream Resolve a hostname Half-close a connection A read timeout UDP send and receive TCP echo, one exchange Serve one HTTP request

38Concurrency0/8Unlock →

future and deref promise and deliver Shared state with an atom locking Parallel map core.async, and a queue Agents Coordinated state with refs

39Unsafe & FFI0/14Unlock →

Java interop Clojure is memory-safe A primitive array An object array Type hints System/arraycopy ByteBuffer into-array and aclone Primitive hints Unchecked math Wrap a byte array areduce Reinterpret double bits Reinterpret float bits

40Commands0/14Unlock →

Command-line arguments An environment variable Env var with a default System properties Current directory Exit with a code All environment variables Count all properties ProcessBuilder Read a line of input Run a command Env for a child Exit status Drain standard input

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