Roman to Integer

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

For example, 2 is written as II in Roman numeral, just two ones added together. 12 is written as XII, which is simply X + II. The number 27 is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

• I can be placed before V (5) and X (10) to make 4 and 9.

• X can be placed before L (50) and C (100) to make 40 and 90.

• C can be placed before D (500) and M (1000) to make 400 and 900.

Given a roman numeral, convert it to an integer.

LeetCode Problem: Link | Click Here

class Solution {
    public int romanToInt(String s) {
        int sum = 0;

        // Iterate through the Roman numeral string
        for (int i = 0; i < s.length(); i++) {
            // Get the current character
            char currentChar = s.charAt(i);
            // Get the next character if it exists, else set it to '\0'
            char nextChar = (i + 1 < s.length() ? s.charAt(i + 1) : '\0');

            // Check for special cases like IV, IX, XL, XC, CD, CM
            if (currentChar == 'I' && nextChar == 'V') {
                sum = sum + 4; // When 'IV' is encountered, add 4 to sum and skip the next character
                i++;
            } else if (currentChar == 'I' && nextChar == 'X') {
                sum = sum + 9; // When 'IX' is encountered, add 9 to sum and skip the next character
                i++;
            } else if (currentChar == 'X' && nextChar == 'L') {
                sum = sum + 40; // When 'XL' is encountered, add 40 to sum and skip the next character
                i++;
            } else if (currentChar == 'X' && nextChar == 'C') {
                sum = sum + 90; // When 'XC' is encountered, add 90 to sum and skip the next character
                i++;
            } else if (currentChar == 'C' && nextChar == 'D') {
                sum = sum + 400; // When 'CD' is encountered, add 400 to sum and skip the next character
                i++;
            } else if (currentChar == 'C' && nextChar == 'M') {
                sum = sum + 900; // When 'CM' is encountered, add 900 to sum and skip the next character
                i++;
            } else {
                // For other cases like 'I', 'V', 'X', 'L', 'C', 'D', 'M', add their respective values to sum
                if (s.charAt(i) == 'I') {
                    sum = sum + 1;
                } else if (s.charAt(i) == 'V') {
                    sum = sum + 5;
                } else if (s.charAt(i) == 'X') {
                    sum = sum + 10;
                } else if (s.charAt(i) == 'L') {
                    sum = sum + 50;
                } else if (s.charAt(i) == 'C') {
                    sum = sum + 100;
                } else if (s.charAt(i) == 'D') {
                    sum = sum + 500;
                } else if (s.charAt(i) == 'M') {
                    sum = sum + 1000;
                }
            }
        }
        return sum;
    }
}