Cassidoo’s Interview question of the week | 452

Learning Resources
1

This week’s question:

You’re building a pizza ordering system that enforces strict ingredient layering rules. Given an array of pizza layers (bottom to top) and a set of rules where each rule states that ingredient A must appear somewhere below ingredient B, write a function that determines whether the pizza is valid. If any rule is violated, return the pair [A, B] that was violated first (in the order the rules are given). If the pizza is valid, return true.

Examples:

layers = ["dough", "sauce", "cheese", "pepperoni", "basil"]
rules = [
  ["sauce", "cheese"],
  ["cheese", "pepperoni"],
  ["dough", "basil"],
];
rules2 = [
  ["cheese", "pepperoni"],
  ["cheese", "sauce"], # "it's under the sauce"
];

validate_pizza(layers, rules);
=> true

validate_pizza(layers, rules2);
=> ["cheese", "sauce"]
1 Like
2

Doing this one because it looked easy… (hope the solution is correct :sweat_smile:)

Solution 
require 'minitest/autorun'

def validate_pizza(layers, rules)
  # We should receive "pairs"...
  raise "Ratatouille!" if rules.any? { _1.length != 2 }

  rules.each do |rule|
    rule => [String => ingredient_below, String => ingredient_above]
    below_idx = layers.index(ingredient_below)
    above_idx = layers.index(ingredient_above)
    raise "Invalid rule: #{rule.inspect}" if below_idx.nil? || above_idx.nil?

    return rule if below_idx > above_idx
  end

  true
end

class TestPizza < Minitest::Test
  def test_validate_pizza
    layers = %w[dough sauce cheese pepperoni basil]

    assert(validate_pizza(layers, [
      %w[sauce cheese],
      %w[cheese pepperoni],
      %w[dough basil]
    ]))

    invalid = %w[cheese sauce]
    assert_equal(invalid, validate_pizza(layers, [
      %w[cheese pepperoni],
      %w[cheese sauce]
    ]))

    invalid = %w[basil dough]
    assert_equal(invalid, validate_pizza(layers, [
      %w[basil dough]
    ]))
  end
end
2 Likes
3
Solution 
def validate_pizza(layers, rules)
  invalidated_rule = rules.find { |ingredient_a, ingredient_b|
    layers.index(ingredient_a) > layers.index(ingredient_b)
  }

  invalidated_rule || true
end
1 Like