1.3 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.

Method

Roman numeric system: https://en.wikipedia.org/wiki/Roman_numerals

for loop each character to get it's value and then do operations according to the rule of roman number.

when the left component > right component, add sum; or right component - left component;

Time and Space Complexity

o(n)

Code

public class Solution {

public int romanToInt(String s) {
    if (s == "" || s.length() == 0){
        return 0;
    }
    int val = 0;
    int pre = 0;
    for (int i = 0; i < s.length(); i++){
         char c = s.charAt(i);
         int cur = helper(c);
         if (cur <= pre){
             val += cur;
         } else {
             val = val - pre + cur - pre;
         }
         pre = cur;
    }
    return val;
}

public int helper(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;
    }
    return 0;
}

}