euler/python/e089.py

CHAR_TO_INT = [
    ('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),
]


def tests():
    assert(numeral_to_integer("XXXXIIIIIIIII") == 49)
    assert(numeral_to_integer("XLIIIIIIIII") == 49)
    assert(numeral_to_integer("XXXXVIIII") == 49)
    assert(numeral_to_integer("XLVIIII") == 49)
    assert(numeral_to_integer("XXXXIX") == 49)
    assert("XLIX" == integer_to_numeral(49))
    assert("MCMXXXVII" == integer_to_numeral(1937))


def integer_to_numeral(integer):
    i = 0
    s = ''
    while integer > 0:
        char, value = CHAR_TO_INT[i]
        while integer >= value:
            s += char
            integer -= value
        i += 1
    assert(integer == 0)
    return s


def numeral_to_integer(numeral):
    i, r = 0, 0
    while numeral and i < len(CHAR_TO_INT):
        char, value = CHAR_TO_INT[i]
        len_char = len(char)
        while len(numeral) >= len_char and numeral[:len_char] == char:
            r += value
            numeral = numeral[len_char:]
        i += 1
    assert(not numeral)
    return r


def save_characters(numeral):
    initial_chars = len(numeral)
    i = numeral_to_integer(numeral)
    new_numeral = integer_to_numeral(i)
    new_chars = len(new_numeral)
    return initial_chars - new_chars


def euler_089():
    tests()

    with open("../txt/e089.txt") as f:
        numerals = map(lambda l: l.strip(), f.readlines())
    return sum(map(save_characters, numerals))


if __name__ == "__main__":
    solution = euler_089()
    print("e089.py: " + str(solution))
    assert(solution == 743)