algorithm_math_romanr_to_integer.java

algorithm_math_romanr_to_integer.java

public class Solution {
    public int romanToInt(String s) {
        int len = s.length();

        s = s + " ";
        int res = 0;
        for (int i = 0; i < len; i++) {
            char ch   = s.charAt(i);
            char nxCh = s.charAt(i+1);
            
            if (ch == 'M') {
                res += 1000;
            } else if (ch == 'C') {
                if (nxCh == 'M') {
                    res += 900;
                    i++;
                } else if (nxCh == 'D') {
                    res += 400;
                    i++;
                } else {
                    res += 100;
                }
            } else if (ch == 'D') {
                res += 500;
            } else if (ch == 'X') {
                if (nxCh == 'C') {
                    res += 90;
                    i++;
                } else if (nxCh == 'L') {
                    res += 40;
                    i++;
                } else {
                    res += 10;
                }
            } else if (ch == 'L') {
                res += 50;
            } else if (ch == 'I') {
                if (nxCh == 'X') {
                    res += 9;
                    i++;
                } else if (nxCh == 'V') {
                    res += 4;
                    i++;
                } else {
                    res++;
                }
            } else { // if (ch == 'V')
                res += 5;
            }
        }
        return res;
    }
}