27. Roman Numerals

Given a Roman numeral less than 4,000, convert it to a decimal number. This Wikipedia article describes Roman numerals in details, but here is a brief description:

Roman numerals consist of the following symbols:

• I is 1

• V is 5

• X is 10

• L is 50

• C is 100

• D is 500

• M is 1,000

A numeral is formed by a sequence of these symbols, where each symbol can be used up to 3 times to contribute to the total. Symbols are ordered left-to-right from larger to smaller, except for the following cases:

• I placed before V or X indicates one less, so 4 is IV (one less than 5) and 9 is IX (one less than 10)

• X placed before L or C indicates ten less, so 40 is XL (ten less than 50) and 90 is XC (ten less than 100)

• C placed before D or M indicates a hundred less, so 400 is CD (a hundred less than 500) and 900 is CM (a hundred less than 1,000)

For example, 11 is XI, 98 is XCVIII, 99 is XCIX and 1944 is MCMXLIV.

romanToDecimal("MMXVI");

2016