java - 将罗马数字转换为十进制

Question

我已经设法让我的代码将大多数罗马数字转换为其适当的十进制值。但它不适用于某些特殊情况。示例:XCIX = 99 但我的代码打印出 109。

这是我的代码。

public static int romanConvert(String roman)
{
    int decimal = 0;

    String romanNumeral = roman.toUpperCase();
    for(int x = 0;x<romanNumeral.length();x++)
    {
        char convertToDecimal = roman.charAt(x);

        switch (convertToDecimal)
        {
        case 'M':
            decimal += 1000;
            break;

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

        case 'C':
            decimal += 100;
            break;

        case 'L':
            decimal += 50;
            break;

        case 'X':
            decimal += 10;
            break;

        case 'V':
            decimal += 5;
            break;

        case 'I':
            decimal += 1;
            break;
        }
    }
    if (romanNumeral.contains("IV"))
    {
        decimal-=2;
    }
    if (romanNumeral.contains("IX"))
    {
        decimal-=2;
    }
    if (romanNumeral.contains("XL"))
    {
        decimal-=10;
    }
    if (romanNumeral.contains("XC"))
    {
        decimal-=10;
    }
    if (romanNumeral.contains("CD"))
    {
        decimal-=100;
    }
    if (romanNumeral.contains("CM"))
    {
        decimal-=100;
    }
    return decimal;
}

Answer 1

逆向遍历就好了。

public class RomanToDecimal {
    public static void romanToDecimal(java.lang.String romanNumber) {
        int decimal = 0;
        int lastNumber = 0;
        String romanNumeral = romanNumber.toUpperCase();
        /* operation to be performed on upper cases even if user 
           enters roman values in lower case chars */
        for (int x = romanNumeral.length() - 1; x >= 0 ; x--) {
            char convertToDecimal = romanNumeral.charAt(x);

            switch (convertToDecimal) {
                case 'M':
                    decimal = processDecimal(1000, lastNumber, decimal);
                    lastNumber = 1000;
                    break;

                case 'D':
                    decimal = processDecimal(500, lastNumber, decimal);
                    lastNumber = 500;
                    break;

                case 'C':
                    decimal = processDecimal(100, lastNumber, decimal);
                    lastNumber = 100;
                    break;

                case 'L':
                    decimal = processDecimal(50, lastNumber, decimal);
                    lastNumber = 50;
                    break;

                case 'X':
                    decimal = processDecimal(10, lastNumber, decimal);
                    lastNumber = 10;
                    break;

                case 'V':
                    decimal = processDecimal(5, lastNumber, decimal);
                    lastNumber = 5;
                    break;

                case 'I':
                    decimal = processDecimal(1, lastNumber, decimal);
                    lastNumber = 1;
                    break;
            }
        }
        System.out.println(decimal);
    }

    public static int processDecimal(int decimal, int lastNumber, int lastDecimal) {
        if (lastNumber > decimal) {
            return lastDecimal - decimal;
        } else {
            return lastDecimal + decimal;
        }
    }

    public static void main(java.lang.String args[]) {
        romanToDecimal("XIV");
    }
}