Roman to Integer

Given a roman numeral, convert it to an integer.

Input is guaranteed to be within the range from 1 to 3999.

class Solution {

public:
    int romanToInt(string s) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        map<char, int> symbols;
        symbols.clear();
        
        symbols[' '] = 0;
        symbols['I'] = 1;
        symbols['V'] = 5;
        symbols['X'] = 10;
        symbols['L'] = 50;
        symbols['C'] = 100;
        symbols['D'] = 500;
        symbols['M'] = 1000;
        
        int length = s.size();
        char currentSymbol;
        char previousSymbol = ' ';
        int solution = 0;
        int digit = 0;
        
        for (int i=0;i<length;++i){
            currentSymbol = s[i];
            if (currentSymbol!=previousSymbol){
                if (symbols[previousSymbol]<symbols[currentSymbol]){
                    solution += -digit;
                    digit = symbols[currentSymbol];
                    previousSymbol = currentSymbol;
                }
                else if (symbols[previousSymbol]>symbols[currentSymbol]){
                    solution += digit;
                    digit = symbols[currentSymbol];
                    previousSymbol = currentSymbol;
                }
            }
            else{// symbol == currentSymbol
                digit += symbols[currentSymbol];
            }
            if (i==length-1)
                solution += digit;
        }
        return solution;
    }
};