Roman to Integer

easyPROMath & DesignMicrosoft DSA

Convert a Roman numeral string to an integer.

I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Subtractive: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900.

Example

Input

III

Output

Reasoning

Input: s is a Roman numeral written as a string of symbols, here III: three copies of the symbol I, each worth $1$ .
Math: a numeral's value is the total of its symbols' values, except inside the six subtractive pairs from the description (IV, IX, XL, XC, CD, CM), where the pair as a whole stands for the difference, e.g. IV $= 5 - 1 = 4$ .
III contains no V, X or any larger symbol, so none of those pairs can occur and every symbol simply adds: $1 + 1 + 1 = 3$ .
Output: the plain integer 3, not a string.
Notice that changing the last symbol to V gives IIV, which is not valid; the valid way to write $4$ is IV, where the I now counts as $-1$ instead of $+1$ .

Constraints

1 <= len(s) <= 15
s is a valid Roman numeral in [1, 3999]

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solution.py

Python 3.13

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Roman to Integer

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