RomanNumeralAddition.cpp

#include<iostream>
#include <string>
#include <unordered_map>

class Solution {
public:
    int romanToInt(std::string s) {

        int sum = 0;
        int length = s.length();

       for(int i = 0; i < length; i++){

        // check for a size of 1 string
        if (length == 1){
            sum += r[s[i]];
        }

        // condition prevents index out of bounds
        if(i == 0) continue; 
        int currentVal = r[s[i]],
            prevVal = r[s[i-1]];
        char currentChar = s[i],
             prevChar = s[i-1];  

        // Subtraction instances are: I before V and X, X before L and C, C before D and M.
        if((currentChar == 'V' || currentChar == 'X') && prevChar == 'I'){
            sum += currentVal - prevVal;
            if(i != length - 2){i++;}
            else {
                sum += r[s[i+1]];
                break;
            }
        }
        else if((currentChar == 'L' || currentChar == 'C') && prevChar == 'X'){
            sum += currentVal - prevVal;
            if(i != length - 2){i++;}
            else {
                sum += r[s[i+1]];
                break;
            }
        }
        else if((currentChar == 'D' || currentChar == 'M') && prevChar == 'C'){
            sum += currentVal - prevVal;
            if(i != length - 2){i++;}
            else {
                sum += r[s[i+1]];
                break;
            }
        }
        // condition where no subtraction conditions are met
        else {
            sum += i == length - 1 ? prevVal + currentVal : prevVal;
        }      
       }
        return sum;
    }
    
private:
    std::unordered_map<char, int> r = {
        {'I', 1},
        {'V', 5},
        {'X', 10},
        {'L', 50},
        {'C', 100},
        {'D', 500},
        {'M', 1000},
    };
};