[LeetCode #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 c2n(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(char* s) {
    int result = 0;
    for(int i = 0; i < strlen(s); i++){
        if ( i>0 && (c2n(s[i]) > c2n(s[i-1]))){
            result += (c2n(s[i]) - 2 * c2n(s[i-1]));
        }else{
            result += c2n(s[i]);   
        }
    }
    
    return result;
}