String Manipulation String Hash Map Counting Character Pattern Matching
Learner Level

Implement the romanNumeralToInteger method that converts a Roman numeral string into an integer.

The input contains a Roman numeral string roman. Your task is to convert it into its integer value.

Roman symbols usually add their values, but when a smaller value appears before a larger value, it must be subtracted. For example, IV is 4 and CM is 900.

Example 1
Input:
roman (string) = MCMXCIV
Return:
(int) 1994
Example 2
Input:
roman (string) = III
Return:
(int) 3
Example 3
Input:
roman (string) = LVIII
Return:
(int) 58

Create a map of Roman symbols and their numeric values.

Scan the string from left to right. If the current symbol is smaller than the next symbol, subtract its value because it is part of a subtractive pair. Otherwise, add its value.

This handles normal additions like VIII and subtractive cases like IX, XL, and CM.

Pseudocode:

function romanNumeralToInteger(roman):
    values = map of I=1, V=5, X=10, L=50, C=100, D=500, M=1000
    total = 0
    for i from 0 to length(roman) - 1:
        current = values[roman[i]]
        next = 0
        if i + 1 < length(roman):
            next = values[roman[i + 1]]
        if current < next:
            total = total - current
        else:
            total = total + current
    return total
Run your code to see the result.