13. Roman to Integer

Given a roman numeral, convert it to an integer.

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

int toNumber(char ch) {
switch (ch) {
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;
}
return 0;
}

int romanToInt(char* s) {
int len = strlen(s);
int ret = 0;

for(int i = 0; i < len; i++){
if(i+1 < len && toNumber(s[i+1]) > toNumber(s[i])){
ret += toNumber(s[i+1]) - toNumber(s[i]);
i++;
}
else ret += toNumber(s[i]);
}
return ret;
}