LeetCode OJ--Roman to Integer

http://oj.leetcode.com/problems/roman-to-integer/

罗马数字到自然数字的转换，先自己查相关的背景知识，然后分析清楚了。可以简化写，嗯嗯。“简化”，抓到本质。

#include <iostream>
#include <map>
#include <string>
using namespace std;

class Solution {
public:
    int change(char ch)
    {
        int num = 0;
        switch(ch)
        {
        case 'I':
            num = 1;
            break;
        case 'V':
            num = 5;
            break;
        case 'X':
            num = 10;
            break;
        case 'L':
            num = 50;
            break;
        case 'C':
            num = 100;
            break;
        case 'D':
            num = 500;
            break;
        case 'M':
            num = 1000;
        }
        return num;
    }
    int romanToInt(string s) {
        int i = 0;
        int sum = 0;
        int num = 1;
        for(i = 0;i<s.size()-1;i++)
        {
            if(change(s[i])<change(s[i+1]))
                sum -= change(s[i]);
            else
                sum += change(s[i]);
        }
        sum += change(s[i]);
        return sum;
    }
};

int main()
{
    Solution myS; 
    myS.romanToInt("DCXXI");
    return 0;
}