题目描述：

Given a roman numeral, convert it to an integer.

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

　　这道题很简单，我就直接贴答案了。

solution1：

int romanToInt(string s) {
    int res = 0;
    char ch;
    int n = s.size();
    s += "#";
    for (int i = 0;i < n;++i)
    {
        ch = s[i];
        switch(ch){
        case 'I':
            if(s[i+1] == 'V' || s[i+1] == 'X')
                res -= 1;
            else
                res += 1;
            break;
        case 'V':
            res += 5;
            break;
        case 'X':
            if(s[i+1] == 'L' || s[i+1] == 'C')
                res -= 10;
            else
                res += 10;
            break;
        case 'L':
            res += 50;
            break;
        case 'C':
            if(s[i+1] == 'D' || s[i+1] == 'M')
                res -= 100;
            else
                res += 100;
            break;
        case 'D':
            res += 500;
            break;
        case 'M':
            res += 1000;
            break;
        default:
            break;
        }
    }
    return res;
}

上面是我自己写的，下面用了map，代码看起来简洁些。
solution2：

int romanToInt(string s) {
    map<char,int> m;
    m['M'] = 1000;
    m['D'] = 500;
    m['C'] = 100;
    m['L'] = 50;
    m['X'] = 10;
    m['V'] = 5;
    m['I'] = 1;
    int result = 0;
    int i;
    for(i = 0;i < s.size()-1;++i) { 
        if(m[s[i]] < m[s[i+1]])
            result -= m[s[i]];
        else
            result += m[s[i]];
    }
    result += m[s[i]];
    return result;
}

 

转载于:https://www.cnblogs.com/gattaca/p/4278057.html