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

For example,2is written asIIin Roman numeral, just two one's added together.12is written asXII, which is simplyX + II. The number27is written asXXVII, which isXX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is notIIII

• Ican be placed beforeV(5) andX(10) to make 4 and 9.
• Xcan be placed beforeL
  (50) andC(100) to make 40 and 90.
• Ccan be placed beforeD(500) andM(1000) to make 400 and 900.

Given a roman numeral, convert it to an integer.

public int romanToInt(String s) {
        char [] str = s.toCharArray();
        int n = s.length();
        int ans = 0;
        for (int i = 0; i < n; i++){
            
 
switch (str[i]){
                case 'M' : ans += 1000;break;
                case 'D' : ans += 500; break;
                case 'C' :
                    if( i + 1 < n && (str[i + 1] == 'M' || str[i + 1] == 'D') ){
                        ans -= 100;
                    }else{
                        ans += 100;
                    }
                    break;
                case 'L' : ans += 50; break;
                case 'X' :
                    if(i + 1 < n && (str[i + 1] == 'C' || str[i + 1] =='L')){
                        ans -= 10;
                    }else{
                        ans += 10;
                    }
                    break;
                case 'V' : ans += 5; break;
                case 'I' :
                    if( i + 1 < n && (str[i + 1] == 'V' || str[i + 1] == 'X')){
                        ans -= 1;
                    }else{
                        ans += 1;
                    }
                    break;
            }
        }
        return ans;
    }

參考連結：

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

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