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| #! /usr/bin/env python | |
| """ | |
| Convert roman numerals. To test: `nosetests roman.py`. | |
| """ | |
| import nose.tools | |
| KNOWN_VALUES = [ | |
| (1, 'I'), | |
| (5, 'V'), | |
| (10,'X'), | |
| (50,'L'), | |
| (100,'C'), | |
| (500,'D'), | |
| (1000,'M'), | |
| (2, "II"), | |
| (3, "III"), | |
| (4, "IV"), | |
| (200,"CC"), | |
| (9, "IX"), | |
| (19, "XIX"), | |
| (49, "XLIX"), | |
| (99, "XCIX"), | |
| (207, "CCVII"), | |
| (1904, "MCMIV"), | |
| (1954, "MCMLIV"), | |
| (2013, "MMXIII"), | |
| (400, "CD"), | |
| (900, "CM"), | |
| (10000, "MMMMMMMMMM"), | |
| ] | |
| SYMBOLS = [ | |
| (1, 'I'), | |
| (5, 'V'), | |
| (10,'X'), | |
| (50,'L'), | |
| (100,'C'), | |
| (500,'D'), | |
| (1000,'M'), | |
| ] | |
| def convert(number): | |
| big_string = number*'I' | |
| return big_string_to_small(big_string) | |
| def big_string_to_small(big_string): | |
| """ | |
| >>> big_string_to_small('I'*1000) | |
| 'M' | |
| >>> big_string_to_small('I'*500) | |
| 'D' | |
| >>> big_string_to_small('I'*100) | |
| 'C' | |
| >>> big_string_to_small('I'*105) | |
| 'CV' | |
| """ | |
| result = big_string | |
| for (number, text) in reversed(SYMBOLS): | |
| if number*'I' in result: | |
| # Replace all runs of "I" with the appropriate symbol | |
| result = result.replace(number*'I',text) | |
| return replace_repeats(result) | |
| def replace_repeats(roman): | |
| """ | |
| >>> replace_repeats('IIII') | |
| 'IV' | |
| >>> replace_repeats('XXXX') | |
| 'XL' | |
| >>> replace_repeats(convert(404)) | |
| 'CDIV' | |
| """ | |
| result = roman | |
| # iterate over all of the symbols, looking two ahead each iteration | |
| symbols = zip(SYMBOLS, SYMBOLS[1:], SYMBOLS[2:]) | |
| for (_, smaller), (_, bigger), (_, BIGGER) in symbols: | |
| # Substitute four consecutive symbols (IIII) for a more simple | |
| # representation (IV). | |
| if 4*smaller in result: | |
| target = "{}{}".format(smaller, bigger) | |
| result = result.replace(4*smaller, target) | |
| # If a pattern like "VIV" exists, there is a more compact | |
| # representation: IX. | |
| aba = "{0}{1}{0}".format(bigger, smaller) | |
| if aba in result: | |
| target = "{}{}".format(smaller, BIGGER) | |
| result = result.replace(aba, target) | |
| result = replace_repeats(result) | |
| return result | |
| def test_known_value(): | |
| for input_, output in KNOWN_VALUES: | |
| yield _check_known_value, input_, output | |
| def _check_known_value(input_, output): | |
| nose.tools.eq_(convert(input_), output) |
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Awesome!