LeetCode 13. Roman to Integer

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本文介绍了一种将罗马数字转换为整数的算法实现，通过解析罗马数字的构成规则，利用哈希映射和比较操作，实现了从1到3999范围内的罗马数字到整数的有效转换。

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Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

For example, two is written as II in Roman numeral, just two one's added together. Twelve is written as, XII, which is simply X + II. The number twenty seven is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

I can be placed before V (5) and X (10) to make 4 and 9.
X can be placed before L (50) and C (100) to make 40 and 90.
C can be placed before D (500) and M (1000) to make 400 and 900.

Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.

Tip：此题为较为简单的模拟，读题转化为计算机语言即可

public class RomanToIntegerSolution {
    public int romanToInt(String s) {
        int result = 0;

        //设置map
        int[] map = new int[128];
        map['I'] = 1;
        map['V'] = 5;
        map['X'] = 10;
        map['L'] = 50;
        map['C'] = 100;
        map['D'] = 500;
        map['M'] = 1000;

        int len = s.length();
        if (len > 1) {

            for (int i = 0; i < len; i++) {
                if (i<len-1) {
                    //可以与后一位比较
                    if (comepare(map[s.charAt(i)], map[s.charAt(i + 1)])) {
                        result += map[s.charAt(i)];

                    } else {
                        result += (map[s.charAt(i + 1)] - map[s.charAt(i)]);
                        i++;
                    }
                }else {
                    //最后一位无须判断
                    result += map[s.charAt(i)];
                }

            }

            return result;
        } else {
            //只有一位就直接返回
            return map[s.charAt(0)];
        }
    }

    private boolean comepare(int x, int y) {
        return x >= y;
    }