Roman to Integer

Description:

Given a roman numeral, convert it to an integer.

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

分析：

1~9: {“I”, “II”, “III”, “IV”, “V”, “VI”, “VII”, “VIII”, “IX”};

10~90: {“X”, “XX”, “XXX”, “XL”, “L”, “LX”, “LXX”, “LXXX”, “XC”};

100~900: {“C”, “CC”, “CCC”, “CD”, “D”, “DC”, “DCC”, “DCCC”, “CM”};

1000~3000: {“M”, “MM”, “MMM”}.

从前往后扫描，用一个临时变量记录分段数字。

如果当前比前一个大，说明这一段的值应该是当前这个值减去上一个值。比如

则，将当前值加入到结果中，然后开始下一段记录。比如 VI = 5 + 1, II=1+1。

代码：

#include <iostream>

using namespace std;

int map(const char c) //罗马字符到整数的映射
{
switch (c) {
case 'I':   return 1;
case 'V':   return 5;
case 'X':   return 10;
case 'L':   return 50;
case 'C':   return 100;
case 'D':   return 500;
case 'M':   return 1000;
default:    return 0;
}
}

int RomanToInteger(string &roman)
{
int result = 0;
for (int i = 0; i < roman.size(); i++) {
if (i > 0 && (roman[i] > roman[i-1]))
result += (map(roman[i]) - 2*map(roman[i-1]));
else
result += map(roman[i]);
}

return result;
}

int main(int argc, char const *argv[]) {
string roman = "VII";
string roman2 = "IX";
string roman3 = "DCC";

std::cout << RomanToInteger(roman) << std::endl;
std::cout << RomanToInteger(roman2) << std::endl;
std::cout << RomanToInteger(roman3) << std::endl;

return 0;
}

测试：