LeetCode: Roman to Integer

Given a roman numeral, convert it to an integer.

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

class Solution {
public:
int map(char c)
{
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 romanToInt(string s) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
int nSize = s.size();
int pre = 1001;
int result = 0;
int cur;
for (int i = 0; i < nSize; ++i)
{
cur = map(s[i]);
result += cur;
if (cur > pre)
{
result -= 2*pre;
}
pre = cur;
}
return result;
}
};