【LeetCode】Roman to Integer

class Solution {
public:
    int romanToInt(string s) {
        int n = 0;
        char lastC = 0;
        for(int i = 0; i < s.size(); i ++)
        {
            switch(s[i])
            {
                case ‘I‘:
                    n += 1;     
                    lastC = s[i];
                    break;
                case ‘V‘:
                    if(lastC == ‘I‘)
                    {//IV
                        n -= 1;
                        n += 4;
                        lastC = 0;
                    }
                    else
                    {
                        n += 5;     
                        lastC = s[i];   
                    }
                    break;
                case ‘X‘:
                    if(lastC == ‘I‘)
                    {//IX
                        n -= 1;
                        n += 9;
                        lastC = 0;
                    }
                    else
                    {
                        n += 10;  
                        lastC = s[i];
                    }
                    break;
                case ‘L‘:
                    if(lastC == ‘X‘)
                    {//XL
                        n -= 10;
                        n += 40;
                        lastC = 0;
                    }
                    else
                    {
                        n += 50;  
                        lastC = s[i];
                    }
                    break;
                case ‘C‘:
                    if(lastC == ‘X‘)
                    {//XC
                        n -= 10;
                        n += 90;
                        lastC = 0;
                    }
                    else
                    {
                        n += 100;   
                        lastC = s[i];   
                    }
                    break;
                case ‘D‘:
                    if(lastC == ‘C‘)
                    {//CD
                        n -= 100;
                        n += 400;
                        lastC = 0;
                    }
                    else
                    {
                        n += 500;
                        lastC = s[i];
                    }
                    break;
                case ‘M‘:
                    if(lastC == ‘C‘)
                    {//CM
                        n -= 100;
                        n += 900;
                        lastC = 0;
                    }
                    else
                    {
                        n += 1000;
                        lastC = s[i];
                    }
                    break;
                default:
                    return 0;
            }
        }
        return n;
    }
};