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Data Structures and Algorithms in Ruby

Q: Which Ruby classes match which data structures?

Array is a dynamic array that serves as a stack (push, pop) and a queue (push, shift); Hash is a hash table that remembers insertion order; and Set, in the standard library, is a hash-based set. That is the list. There is no heap, priority queue, linked list, tree, trie or graph, so those you build yourself, in steps one and two.

Ruby gives you Array, Hash and Set, and no heap, priority queue, linked list or tree. This path has you build each missing structure in Ruby, where a traversal is one each block, then sort, recurse and search graphs with them, and finish on graded interview problems. Free, in your browser, with a certificate on most courses.

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377 lessons228 challenges702 quiz questions

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DSA in Ruby, step by step

38 courses377 lessons228 challenges702 quiz questions

Each step is a set of existing Coddy courses, and every Start button opens them in Ruby. The three courses not taught in Ruby yet are listed after the steps.

1
Step 1
Data Structures Series, part one
Start this stepStartStack, queue, binary tree, hash table and linked list, each built from scratch in Ruby and then used to solve problems. After it, Array as a stack or a queue, and Hash as a lookup table, are choices you can explain rather than habits.Start
5 courses, in order
66 lessons34 challenges
2
Step 2
Data Structures Series, part two
Start this stepStartDoubly linked list, heaps and priority queues, tries, graphs and the self-balancing AVL tree: everything past Array, Hash and Set that Ruby leaves to you. The heap you write here is the priority queue the graph step needs.Start
5 courses, in order
72 lessons42 challenges
3
Step 3
Sorting algorithms
Start this stepStartBubble, selection, insertion, merge, quick, heap, counting and radix sort, written in Ruby and watched in the visualizer. Array#sort makes no promise of stability; after this step you know which of the eight sorts could have made one.Start
8 courses, in order
74 lessons31 challenges319 questions
4
Step 4
Recursive thinkingDedicated page
Start this stepStartRecursion challenges in Ruby. A runaway recursion raises SystemStackError (stack level too deep), and Ruby does not optimize tail calls by default, so depth is worth watching even in a language this forgiving. Dynamic programming and bit manipulation are listed after the steps, since they are taught in Python and C++.Start Dedicated page15 lessons15 challenges
5
Step 5
Graph algorithms
Start this stepStartBreadth-first and depth-first search, Dijkstra, Bellman-Ford, topological sort, Kruskal and Prim in Ruby, on the graph you built in step two. Ruby has no priority queue, so the heap from step two is the one Dijkstra needs.Start
7 courses, in order
63 lessons21 challenges383 questions
6
Step 6
Interview practice
Start this stepStartTen interview challenge packs and two coding-problem banks in Ruby, graded by test cases: unfamiliar problems, solved without a tutorial, with blocks and hashes whose cost you now know.Start
12 courses, in order
87 lessons85 challenges

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Intro to Variables

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A variable is a named container that stores a value you can reference later in your program.

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Why learn DSA in Ruby on Coddy

The structures Ruby leaves out. Array is a stack and a queue at once, Hash a hash table that keeps insertion order, and Set sits in the standard library; past that, there is no heap, priority queue, linked list or tree. When a Ruby interview problem needs one, you are expected to write it, and on this path you do.
Short code, readable algorithms. Blocks and Enumerable (each, map, select, reduce) keep a traversal to a line or two, so a breadth-first search or a merge reads almost like pseudocode. Just remember that each of those calls is a loop with a cost, which is what this path teaches you to count.
Nearly the whole path in Ruby. Every data structure, sort, graph algorithm, recursion challenge and interview pack is taught in Ruby. Three are taught elsewhere and listed after the steps with a link to each: dynamic programming and the Python interview series in Python, and bit manipulation in C++. Bit manipulation is an easy read from Ruby, which has the same operators, on integers that never overflow.
Graded like an interview. Every lesson ends in a Ruby challenge checked by test cases, and when one fails, Bugsy reads your code and nudges you toward the fix without handing over the answer. A free certificate on most courses, each verifiable at its own URL.

Frequently asked questions about DSA in Ruby

Is Ruby good for data structures and algorithms?

Yes, for learning and for interviews at Rails companies: the code is as short as Python's, and blocks make traversals read like the algorithm. Two gaps are worth knowing. The standard library has no heap, priority queue, linked list or tree, so you write them; and Array#sort does not promise stability, so when equal elements must keep their order, sort by a pair: sort_by.with_index { |x, i| [x, i] }.

Which Ruby classes match which data structures?

Array is a dynamic array that serves as a stack (push, pop) and a queue (push, shift); Hash is a hash table that remembers insertion order; and Set, in the standard library, is a hash-based set. That is the list. There is no heap, priority queue, linked list, tree, trie or graph, so those you build yourself, in steps one and two.

How do I write a priority queue in Ruby?

Ruby never shipped one, so there are three honest answers: sort the array after each insert, O(n log n) per push; keep it sorted with bsearch_index and insert, O(n) per push; or write a binary heap on an Array, O(log n) for both push and pop. The third is what an interviewer is looking for, and step two has you build it.

Why does insertion order in a Ruby `Hash` matter for algorithms?

Because it turns some classic designs into a few lines. An LRU cache, a favorite interview problem, is a Hash in which a read deletes and reinserts the key to move it to the end, and eviction is shift, which removes the oldest entry. In most languages that takes a hash table plus a doubly linked list, the structures you build in steps one and two, so you can explain what Ruby is doing for you.

Which courses on this path are not taught in Ruby?

Three: dynamic programming and the Python interview series, taught in Python, and bit manipulation, taught in C++. They are listed after the steps, each with a link that opens it in its own language. A memo in Ruby can be a Hash with a default block, as in Hash.new { |h, n| h[n] = n < 2 ? n : h[n - 1] + h[n - 2] }, and n[i] reads bit i of an integer directly, where C++ writes (n >> i) & 1.

Do I need to know Ruby before starting this path?

Methods, blocks, arrays, hashes and classes, at least. If those are new, Coddy's Ruby course takes you there first, free, and this path picks up where it ends.

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