LeetCode13 roman to integer

Given a roman numeral, convert it to an integer.

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

从低位开始累加，注意一下像IV和 VI  DC和CD的处理

class Solution {
public:
    int romanToInt(string s) 
    {
            int sStart = 0;
    int sEnd   = s.size() - 1;
    int pScan   = sEnd;

    int total = 0;

    if(sEnd < 0)
    {
        return -1;
    }

    while(pScan >= sStart)
    {
        if(s[pScan] == 'X' && total < 50)
        {
            total += 10;
            pScan--;
        }
        if(s[pScan] == 'X' && total >= 50)
        {
            total -= 10;
            pScan--;
        }
        else if(s[pScan] == 'V')
        {
            total += 5;
            pScan--;
        }
        else if(s[pScan] == 'I' && total < 5)
        {
            total += 1;
            --pScan;
        }
        else if(s[pScan] == 'I' && total >= 5)
        {
            total -= 1;
            --pScan;
        }
        else if(s[pScan] == 'L')
        {
            total += 50;
            pScan--;
        }
        else if(s[pScan] == 'C' && total < 500)
        {
            total += 100;
            pScan--;
        }
        else if(s[pScan] == 'C' && total >= 500)
        {
            total -= 100;
            pScan--;
        }
        else if(s[pScan] == 'D')
        {
            total += 500;
            pScan--;
        }
        else if(s[pScan] == 'M')
        {
            total += 1000;
            pScan--;
        }
    }
    return total;
        
        
    }
};

if else 语句略长。