LeetCode刷题EASY篇罗马数字转换为整型数字表示

题目

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.

Example 1:

Input: "III"
Output: 3

Example 2:

Input: "IV"
Output: 4

Example 3:

Input: "IX"
Output: 9

Example 4:

Input: "LVIII"
Output: 58
Explanation: L = 50, V= 5, III = 3.

Example 5:

Input: "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

解法

比较简单，只需要注意减法的情况就可以了，暂时想到比较简单的解法。减法情况整理如下：

LeetCode刷题EASY篇罗马数字转换为整型数字表示

class Solution {
    public int romanToInt(String s) {
      {
        if (s == null || s.length() == 0){
            return -1;
        }
        Map<Character, Integer> map = new HashMap<Character, Integer>();
        map.put('I', 1);
        map.put('V', 5);
        map.put('X', 10);
        map.put('L', 50);
        map.put('C', 100);
        map.put('D', 500);
        map.put('M', 1000);
        int result=0;
        for(int i=0;i<s.length();i++){
            Integer current=map.get(s.charAt(i));
            Integer next=0;
            if (i!=s.length()-1){
                 next=map.get(s.charAt(i+1)); 
            }
            if (current==1&&(next==5||next==10)){
                result-=current;
            }
            else if(current==10&&(next==50||next==100)){
                result-=current;
            }
            else  if (current==100&&(next==500||next==1000)){
                result-=current;
            }
            else{
                result+=current;
            }
        }
        return result;

    }  
    }
}