原题链接: https://oj.leetcode.com/problems/roman-to-integer/

// I(1) V(5) X(10) L(50) C(100) D(500) M(1000)
public int romanToInt(String s) {
    if (s == null) return 0;

    s = s.trim();

    if (s.equals("")) return 0;

    int num = 0;
    int length = s.length();
    char cur;
    char next;

    for (int i = 0; i < length; i++) {
        cur = s.charAt(i);

        switch (cur) {
            case 'I':
                if (i + 1 != length) {
                    next = s.charAt(i + 1);

                    if (next == 'V') {
                        num += 4;
                        i++;
                        continue;
                    } else if (next == 'X') {
                        num += 9;
                        i++;
                        continue;
                    }
                }

                num += 1;

                break;

            case 'V':
                num += 5;

                break;

            case 'X':
                if (i + 1 != length) {
                    next = s.charAt(i + 1);

                    if (next == 'L') {
                        num += 40;
                        i++;
                        continue;
                    } else if (next == 'C') {
                        num += 90;
                        i++;
                        continue;
                    }
                }

                num += 10;

                break;

            case 'L':
                num += 50;

                break;

            case 'C':
                if (i + 1 != length) {
                    next = s.charAt(i + 1);

                    if (next == 'D') {
                        num += 400;
                        i++;
                        continue;
                    } else if (next == 'M') {
                        num += 900;
                        i++;
                        continue;
                    }
                }

                num += 100;

                break;

            case 'D':
                num += 500;
                break;

            case 'M':
                num += 1000;
                break;
        }
    }

    return num;
}