LeetCode—— 13. Roman to Integer

题目原址

https://leetcode.com/problems/roman-to-integer/description/

题目描述

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

解题思路

罗马数字一共有7个字母

M	D	C	L	X	V	I
1000	500	100	50	10	5	1

1. 将字符串每个字符转换为对应罗马数字代表的整数
2. 按照罗马数字的组合规则，如果前面的字符小于后面字符的值，则用后面的数减去前面的数为该罗马数字的整数值；如果前面的字符大于后面字符的值，则用后面的数加上前面的数为该罗马数字的整数值。如IV的值为4，VI的值为6

AC代码

class Solution {
    public int romanToInt(String s) {
        int ret = 0;
        int[] a = new int[s.length()];
        for(int i = 0; i < s.length(); i++) {
            switch(s.charAt(i)) {
                case 'M':
                    a[i] = 1000;
                    break;
                case 'D':
                    a[i] = 500;
                    break;
                case 'C':
                    a[i] = 100;
                    break;
                case 'L':
                    a[i] = 50;
                    break;
                case 'X':
                    a[i] = 10;
                    break;
                case 'V':
                    a[i] = 5;
                    break;
                case 'I':
                    a[i] = 1;
                    break;
            }
        }

        for(int i = 0;i<s.length()-1;i++) {
            if(a[i] < a[i+1])
                ret -= a[i];
            else
                ret += a[i];
        }
        return ret + a[s.length()-1];
    }
}

感谢

https://leetcode.com/problems/roman-to-integer/discuss/6509/7ms-solution-in-Java.-easy-to-understand