- 01Getting Started
- 02Your First Output (puts)
- 03Working with Variables
- 04Conditionals (if statements)
- 05Loops
- 06Writing a Method (Function)
- 07Working with Arrays
- 08Loops (while statements)
- 09Classes (Object-Oriented Programming)
- 10Error Handling (begin...rescue)
- 11Handy Array Methods
- 12Recursive Functions
- 13Using the Standard Library
- 14The case/when Statement
- 15The Ternary Operator
- 16Inheritance (Extending a Class)
- 17Writing Comments
- 18Logical Operators (AND, OR, NOT)
- 19Constants (names starting with a capital)
- 20Splitting and Joining Strings (split, join)
- 21Writing nil-Safe Code
- 22Searching an Array (include?)
- 23Transforming an Array (map)
- 24Two-Dimensional Arrays (Tabular Data)
- 25Writing a Custom Exception Class
- 26Default Parameter Values
- 27Working with Set
- 28Testing with Your Own assert Method
- 29Higher-Order Functions (Passing a Block)
- 30Stacks and Queues (Basic Data Structures)
- 31Type Conversion (Casting) Basics
- 32Intro to Regular Expressions (Pattern Matching)
- 33The Binary Search Algorithm
- 34Building a Caesar Cipher (a Character-Shifting Cipher)
- 35Understanding How Bubble Sort Works
- 36Building and Displaying Dates (Basic Year/Month/Day Operations)
- 37Writing Multiple Test Cases Together
- 38Speeding Up Calculations with Memoization (Caching)
- 39Normalizing Strings (strip, Unifying Case)
- 40Shallow Copy vs. Deep Copy
- 41Enum Basics
- 42Flattening an Array
- 43Reversing a String and Checking for Palindromes
- 44Pairing Up Two Arrays (the zip operation)
- 45Rounding Numbers (floor, ceil, round)
- 46Multi-Line Strings (Heredoc)
- 47Methods That Return Multiple Values
- 48Finding the GCD and LCM
- 49Formatting Numbers (Padding Digits, Decimal Places)
- 50Cleanup Logic with begin/rescue/ensure
- 51Methods That Work with Any Type
- 52File Reading and Writing Basics
- 53Generating Random Numbers
- 54Bitwise Operators (AND, OR, XOR, shifts)
- 55Reading Command-Line Arguments
- 56Waiting for a Fixed Amount of Time (sleep)
- 57Watch Out for Floating-Point Rounding Errors
- 58Reading from Standard Input
- 59FizzBuzz (the Classic Practice Problem)
- 60Checking Whether a Number Is Prime
- 61Set Operations with Set (Union, Intersection, Difference)
- 62Converting Number Bases (Binary, Hex)
- 63Checking Balanced Parentheses (an Application of Stacks)
- 64Checking Whether Two Words Are Anagrams
- 65Checking Whether a Year Is a Leap Year
- 66Converting Temperature (Celsius to Fahrenheit)
- 67Prime Factorization
- 68[Applied] Build a Simple Inventory Management Tool
Finding the GCD and LCM
In this lesson you will learn to find the greatest common divisor and least common multiple with Ruby's built-in gcd and lcm methods. This is for anyone searching for "Ruby gcd lcm how to use".
Ruby provides .gcd (greatest common divisor) and .lcm (least common multiple) as integer methods out of the box. Internally they use the Euclidean algorithm, which dates back to antiquity.
The sample code finds the GCD with 12.gcd(18) and the LCM with 4.lcm(6), each in a single method call. Notice how the whole thing is handled by the standard library, with no algorithm to implement yourself.
A common stumbling block for beginners is wondering why this is so easy. Using the built-in method is faster and safer than writing your own, and it is a good illustration of how complete Ruby's standard library is. Implementing it yourself is still worthwhile practice if you want to understand the mechanism.
For three or more numbers, combining it with reduce does the job. It is a good demonstration of how much the standard library covers, even for mathematical work.
๐งช This site can't compile or run Ruby directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser โ nothing is sent anywhere).