Recipe Calculator

Level: Beginner 15–30 min

Concepts: Edge CasesAlgorithms

Solutions: C# | TypeScript | Python

Implement a recipe calculator that can scale ingredients and convert between different units of measurement. The system should handle various types of ingredients and provide accurate conversions.

Requirements

  1. Scale recipes
    • Multiply or divide ingredient quantities
    • Maintain proper proportions
    • Handle fractional amounts
    • Round to appropriate precision
  2. Convert units
    • Convert between metric and imperial units
    • Handle volume and weight conversions
    • Convert between different measurement systems
    • Handle special cases (e.g., temperature)
  3. Validate inputs
    • Check for valid quantities
    • Validate unit conversions
    • Handle edge cases
    • Provide meaningful error messages

Hint

Start by implementing basic scaling and unit conversion, then add more complex features. Consider using a conversion table or matrix for unit conversions. Think about:

  • Precision and rounding rules
  • Common conversion factors
  • Input validation strategies
  • Error handling approaches
  • Zero or negative ingredient quantities
  • Rounding errors in conversions

Bonus

  • Add support for dietary restrictions
  • Implement ingredient substitution
  • Create a shopping list generator
  • Add nutritional information calculation
  • Support multiple languages and regional units

Reference Walkthrough

Reference implementations in C#, TypeScript, and Python live at tddbuddy-reference-katas/recipe-calculator. Eight scenarios cover the core scaling arithmetic: empty recipes, single- and multi-ingredient recipes, the identity factor 1, the zeroing factor 0, fractional quantities, and rejection of negative factors. The API in all three languages is the same shape: scale(recipe, factor) takes a map of ingredient name → quantity and returns a new map with every quantity multiplied by the factor. The kata’s bonus tracks (unit conversion, dietary restrictions, substitutions, shopping lists, nutrition) are out of scope — unit conversion is already demonstrated by the sibling Metric Converter kata.

This kata ships in Agent Full-Bake mode at high gear (F1 tier): the scaling arithmetic is small enough to land as one commit per language, with a brief walkthrough noting there are no builders because the inputs and outputs — an ingredient→quantity map and a numeric factor — are the domain. See the repo’s Gears section for when high gear is the right call.