42 lines
1.4 KiB
Python
42 lines
1.4 KiB
Python
"""
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This program converts a string that represents a valid roman number to its decimal equivalent.
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If the string is not a valid roman number, raises a ValueError exception.
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Time Complexity : O(n)
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Space Complexity : O(1)
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"""
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equivalence = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
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def is_valid_roman_string(roman_number: str) -> bool:
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"""Returns True if all characters of the given string are valid roman numbers"""
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return set(roman_number).issubset(equivalence.keys())
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def conversion(roman_number: str) -> int:
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"""Traverses a given roman number and returns its decimal equivalent"""
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digits = len(roman_number)
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result = 0
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for i, char in enumerate(roman_number):
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if i < digits - 1 and equivalence[char] < equivalence[roman_number[i + 1]]:
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result -= equivalence[char]
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else:
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result += equivalence[char]
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return result
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def roman_to_int(roman_number: str) -> int | ValueError:
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"""Main function"""
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if not is_valid_roman_string(roman_number):
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raise ValueError(f'The string must contain only valid roman numbers: {equivalence.keys()}')
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return conversion(roman_number)
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if __name__ == '__main__':
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print(roman_to_int('MCMXCIV'))
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# 1994
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print(roman_to_int('abc'))
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# ValueError: The string must contain only valid roman numbers: dict_keys(['I', 'V', 'X', 'L', 'C', 'D', 'M'])
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