Validate Roman Numeral

Problem

Return True if the string is a valid Roman numeral in the standard range 1 to 3999, and False otherwise.

Parse the numeral using the subtractive rule, then convert the parsed value back to Roman form and compare with the input; canonical round-tripping rejects repetitions like IIII and invalid pairs like IC. The empty string is invalid.

Hint

Round-tripping through the canonical Roman form catches every invalid numeral.

Test cases

case 1

in: ["III"]

expected: true

case 2

in: ["IV"]

expected: true

case 3

in: ["IIII"]

expected: false

case 4

in: ["MCMXCIV"]

expected: true

case 5

in: ["IC"]

expected: false

case 6

in: [""]

expected: false

Starter codePython

def valid_roman(s):
    # Your code here
    pass

6 test cases · run your code against them in the editor