Integer to roman numeral - Solutions
====================================

.. contents:: :local:

.. _pwp-i2rn-ex1:

Exercise
--------


Solution
^^^^^^^^

.. interactive_code_block:: 
   :caption: A function that converts an integer to a roman numeral

   def integer_to_roman_numeral(integer):
       """Convert an integer to a roman numeral."""
       # Create a dict with the roman symbols and their integer values
       roman_symbols = {                'M':1000,
           'CM':900, 'D':500, 'CD':400, 'C': 100, 
           'XC': 90, 'L': 50, 'XL': 40, 'X':  10,
           'IX':  9, 'V':  5, 'IV':  4, 'I':   1 }
       # Create a variable to be able to add the roman symbols
       roman_numeral = ''
       # Substract the values of the roman symbols as long as the integer is greater then 0
       while integer > 0:
           # Iterate over the dict with the roman symbols
           for roman_symbol, value in roman_symbols.items():
               # Calculate how many times the roman symbol has to be added
               repetitions = integer // value
               # Add the symbol(s) to the result
               roman_numeral += roman_symbol * repetitions
               # Substract the values from the integer
               integer -= value * repetitions

       return roman_numeral


   # Create a dict with test values
   test_values = {'CXXIII': 123, 'CCCXXI':321, 'CDXLIV':444, 'CMXCIX': 999, 'MMXXI': 2021}

   # Print a table with test values and the result of the function
   print('   Test values  | Result')
   print('----------------+-------')
   for roman_numeral, integer in test_values.items():
       print('{:6} | {:>6} | {:>6}'.format(integer, roman_numeral, integer_to_roman_numeral(integer)))


Shorter but less explicit solution
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The code above can be shortened by using less variables but, since *only* the variable ``repetitions`` can be removed and it's important to use round brackets ``(integer // value)`` to maintain the order of precedence of the operators, the overall benefit is small.

.. interactive_code_block:: 
   :caption: A function that converts an integer to a roman numeral - shorter but less explicit solution

   def integer_to_roman_numeral(integer):
       """Convert an integer to a roman numeral."""
       # Create a dict with the roman symbols and their integer values
       roman_symbols = {                'M':1000,
           'CM':900, 'D':500, 'CD':400, 'C': 100, 
           'XC': 90, 'L': 50, 'XL': 40, 'X':  10,
           'IX':  9, 'V':  5, 'IV':  4, 'I':   1 }
       # Create a variable to be able to add the roman symbols
       roman_numeral = ''
       # Substract the values of the roman symbols as long as the integer is greater then 0
       while integer > 0:
           # Iterate over the dict with the roman symbols
           for roman_symbol, value in roman_symbols.items():
               # Add the symbol(s) to the result
               roman_numeral += roman_symbol * (integer // value)
               # Substract the values from the integer
               integer -= value * (integer // value)

       return roman_numeral


   # Create a dict with test values
   test_values = {'CXXIII': 123, 'CCCXXI':321, 'CDXLIV':444, 'CMXCIX': 999, 'MMXXI': 2021}

   # Print a table with test values and the result of the function
   print('   Test values  | Result')
   print('----------------+-------')
   for roman_numeral, integer in test_values.items():
       print('{:6} | {:>6} | {:>6}'.format(integer, roman_numeral, integer_to_roman_numeral(integer)))