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Ruby

695 problems50 sections📅 2026 curriculum

Learn Ruby by typing expressive, idiomatic code.

Practice Ruby's expressive style by typing it: blocks and yield, symbols, the Enumerable methods (map, select, reduce), and a taste of metaprogramming. Each snippet is idiomatic Ruby, and an AI tutor explains every line — how a block differs from a proc, why everything is an object — so the language's joy comes through as you build typing speed.

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Run Ruby on your machine

1. Install the toolchain

brew install ruby # or: sudo apt install ruby

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

ruby hello.rb

Official install docs ↗

progress by section

1Fundamentals0/16start →

Printing if / elsif / else Interpolation Numbers times Variables Big integers case / when Methods Ranges Ternary unless until upto while Keyword arguments

2Strings In Depth0/19start →

Case Interpolation Repeat chars Concatenate each_char Search Join Slice by index Split start_with? / end_with?Trim sub Bang methods format gsub Pad Slice by range tr and count

3Values & References0/16start →

Aliasing freeze Numbers are value-like object_id Return new vs mutate dup for independence dup is shallow equal? vs ==Mutation through a reference Rebinding a parameter Symbols are interned dup vs clone eql? and hashing freeze is shallow Unfreeze via dup Frozen string literals

4Slices & Arrays0/16Unlock →

count first and last include? and index Start and length Range slice reverse Negative indexes rotate sort and sort_by Sort descending take and drop values_at each_cons each_slice partition Slice assignment

5Data structures0/13Unlock →

Array basics Hash basics Clean up an array Array methods Hash methods Symbol keys Array as a queue Set Array as a stack tally Counting hash Nested structures Struct

6Iterators0/20Unlock →

7Traits0/20Unlock →

8Generics0/20Unlock →

9Lifetimes0/20Unlock →

10Closures0/20Unlock →

11Pattern Matching0/20Unlock →

12Error Handling0/21Unlock →

13Option & Result0/20Unlock →

14Conversions0/15Unlock →

to_i and to_f Value to string Array()chars and join chr and ord Integer() and Float()String()to_a to_h Parse in another base Integer to another base format / sprintf Integer(str, base)Array#pack String#unpack

15Collection Conversions0/19Unlock →

Hash keys Hash values uniq Array of pairs to Hash Array to Set flatten Set to sorted Array sort sort_by tally Build a Hash with each_with_object flat_map group_by Invert a Hash Set difference Set intersection Set union uniq with a key Two arrays to a Hash

16Math0/14Unlock →

Integer arithmetic min, max, clamp Math constants Roots and powers Rounding Factorial GCD and LCM Logarithms and exp Min and max of an array Trigonometry hypot and atan2 Modular exponentiation Primes Mean, median, stdev

17Encoding0/22Unlock →

18Random0/20Unlock →

19Data I/O0/18Unlock →

Parse CSV rows Generate JSON Parse JSON Tab-separated values Build a CSV string Select one column CSV with headers CSV to a number matrix Pretty-print JSON Whitespace matrix Read a file whole Skip blanks and comments Print an aligned table Write a matrix as text Stream lines Parse key=value config Round-trip write and read Drop unparseable rows

20Linear Algebra0/21Unlock →

21Text Processing0/16Unlock →

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

22Date & Time0/12Unlock →

Date today Leap year Time now Format a time Day of week Date and time arithmetic Days between dates Epoch conversions Seconds to HH:MM:SS Parse a timestamp Parse with a pattern Parse a clock string

23Memory0/12Unlock →

Swap without a temp freeze for immutability object_id and equal?Symbols are interned dup vs clone equal? vs eql? vs ==Immediate integers Shallow copy shares nesting Deep copy with Marshal Frozen string literals Measuring object size A weak reference

24Modules0/20Unlock →

25Macros0/20Unlock →

26Testing0/20Unlock →

27Algorithms0/8Unlock →

Greatest common divisor Binary search Palindrome check Fibonacci with memoization Merge two sorted arrays Fisher-Yates shuffle Two sum Quicksort

28Sorting Algorithms0/12Unlock →

Built-in sort and sort_by Bubble sort Insertion sort min_by, max_by, and friends Selection sort Counting sort Sorting with the spaceship operator Merge sort Shell sort Quicksort Radix sort Heapsort

29Expression Parsing0/6Unlock →

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

30Idioms0/9Unlock →

String interpolation Blocks over loops each_with_object Keyword arguments Safe navigation and ||=Symbol#to_proc chains tap and then Pattern matching Comparable mixin

31OOP & Traits0/8Unlock →

attr_accessor and friends Class and initialize Class methods with self.Composition over inheritance Inheritance and super Polymorphism via duck typing Struct and Data.define private and protected

32Trait Objects0/14Unlock →

A method taking any speaker An array of mixed objects Return one of several types Collect a mark from each Two names, one object Dispatch by class An array of lambdas Shared default method A pipeline of callables respond_to? capability check Total over mixed shapes Comparable across types A handler registry A module including a module

33Design Patterns0/14Unlock →

Memoize with ||=Adapter object Block builder Constructor injection Block subscribers Singleton mixin Strategy lambdas Command with undo Decorator classes Factory method Connection pool dup with initialize_copy State objects Thread + Queue actor

34Async0/3Unlock →

An Enumerator as a generator A Fiber as a coroutine Drive many tasks to completion

35File I/O0/6Unlock →

Read a file Write a file Append to a file Count lines Read lines lazily Buffered writing in a block

36Filesystem0/18Unlock →

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

37Networking0/16Unlock →

Build a socket address Parse the request line Route by path Classify an IP 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 →

Spawn a thread Capture data in a thread Shared state with a Mutex Message passing with a Queue Atomics and the GVL Threads over local data Guard readers with a Mutex

39Unsafe & FFI0/14Unlock →

A method with a contract A method as a value No raw pointers Exporting to C NUL-terminated bytes Call libc strlen Mutable global state Reinterpret bytes Byte-level indexing Bytes as a slice A managed C pointer Delay initialization Reinterpret the bits Overlapping views

40Commands0/14Unlock →

Iterate the user's args Command-line arguments Env var with a default Read an environment variable Current directory Iterate all env vars Set and remove a variable Exit with a code Path to this script Pass env to a child Run a command 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