挑戰 Codewars LV3 題目

題目(Calculator)：

Create a simple calculator that given a string of operators (), +, -, *, / and numbers separated by spaces returns the value of that expression

Example:

Calculator.new.evaluate("2 / 2 + 3 * 4 - 6") # => 7
Remember about the order of operations! Multiplications and divisions have a higher priority and should be performed left-to-right. Additions and subtractions have a lower priority and should also be performed left-to-right.

class Calculator
  def evaluate(string)
  end
end

calc = Calculator.new

Test.assert_equals(calc.evaluate("4 + 5"), 9)
Test.assert_equals(calc.evaluate("4 * 5"), 20)
Test.assert_equals(calc.evaluate("4 / 5"), 0.8)
Test.assert_equals(calc.evaluate("4 - 5"), -1)
Test.assert_equals(calc.evaluate("4 + 5 * 6"), 34)

影片解題：

答案：

# Calculator
class Calculator
  def evaluate(string)
    ['+', '-', '*', '/'].each do |cal|
      if string.include?(cal)
        return string.split(cal).map{ |x| evaluate(x) }.inject(cal.strip)
      end
    end
    string.to_f
  end
end

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