C#函数转换数字

Question

我正在尝试编写一个实用的函数来将罗马数字输入转换为十进制。我之前已经通过 Javascript 在两个方向上做到了，但是在 C# 版本中我的循环中的 while 迭代有问题，我还不知道如何让它工作。

class ToRoman
{
    public static int RomanToDecimal(string romanNums)
    {
        int result = 0; 

        int[] deci = new int[] {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
        string[] roman = new string[] {"M", "CM", "D", "CD", "C", "XD", "L", "XL", "X", "IX", "V", "IV", "I"};

        for (int i = 0; i < deci.Length; i++)
        {
            while (romanNums.IndexOf(roman[i] == romanNums[i])
            {
                result += deci[i];
                romanNums = romanNums.Replace(roman[i]," ");
            }
        }
        return result;
    }

    static void Main()
    {
        Console.WriteLine(RomanToDecimal("V"));
        Console.WriteLine(RomanToDecimal("XIX"));
        Console.WriteLine(RomanToDecimal("MDXXVI"));
        Console.WriteLine(RomanToDecimal("MCCCXXXVII"));
    }
}

Answer 1

你的方法的第一个问题是你必须使用贪心算法：如果你有，说CDL 输入您应该将其视为 CD + L == 450，而不是 C + D + L == 650。另一个（可能是次要的）问题是您允许不正确的输入，例如 DD 或 IIV、XM 等

可以在 FSA[=43= 的帮助下编写具有 语法检查 的准确实现]（有限状态自动机）。例如。这些输入在语法上不正确：

MIM, LL, XLX, CDC, XXXX, CCCXCX, CCCXL, VL, VX

像这样：

private static Dictionary<char, int> s_Romans = new Dictionary<char, int>() { {'M', 1000}, {'D', 500}, {'C', 100}, {'L', 50}, {'X', 10}, {'V', 5}, {'I', 1}, }; private static int RomanToArabic(string value) { if (null == value) throw new ArgumentNullException("value"); else if (string.IsNullOrWhiteSpace(value)) throw new ArgumentException("Empty or WS only value is not allowed.", "value"); int v; int[] values = value .Select(c => s_Romans.TryGetValue(c, out v) ? v : -1) .ToArray(); int result = 0; int current = 1000; int count = 0; for (int i = 0; i < values.Length; ++i) { v = values[i]; if (v < 0) throw new FormatException($"Invalid symbol {value[i]} at {i + 1}"); else if (v > current) throw new FormatException($"Invalid symbol {value[i]}"); else if (current == v) { count += 1; if (count > 1 && (v == 5 || v == 50 || v == 500)) throw new FormatException($"Invalid symbol {value[i]} at {i + 1}"); else if (count > 3 && current != 1000) throw new FormatException($"Invalid symbol {value[i]} at {i + 1}"); } else { count = 1; current = v; } if (i < value.Length - 1) if (v == 1 || v == 10 || v == 100) if (v * 5 == values[i + 1] || v * 10 == values[i + 1]) { v = values[i + 1] - v; count = 3; i += 1; } result += v; } return result; }

一些测试：

// 4000 Console.Write(RomanToArabic("MMMM")); // 1444 Console.Write(RomanToArabic("MCDXLIV")); // 1009 Console.Write(RomanToArabic("MIX")); // 1 Console.Write(RomanToArabic("I"));

更多测试：

Converting integers to roman numerals

// Mosè Bottacini's code see the link above public static string ToRoman(int number) { if ((number < 0) || (number > 3999)) throw new ArgumentOutOfRangeException("insert value between 1 and 3999"); if (number < 1) return string.Empty; if (number >= 1000) return "M" + ToRoman(number - 1000); if (number >= 900) return "CM" + ToRoman(number - 900); if (number >= 500) return "D" + ToRoman(number - 500); if (number >= 400) return "CD" + ToRoman(number - 400); if (number >= 100) return "C" + ToRoman(number - 100); if (number >= 90) return "XC" + ToRoman(number - 90); if (number >= 50) return "L" + ToRoman(number - 50); if (number >= 40) return "XL" + ToRoman(number - 40); if (number >= 10) return "X" + ToRoman(number - 10); if (number >= 9) return "IX" + ToRoman(number - 9); if (number >= 5) return "V" + ToRoman(number - 5); if (number >= 4) return "IV" + ToRoman(number - 4); if (number >= 1) return "I" + ToRoman(number - 1); throw new ArgumentOutOfRangeException("something bad happened"); } ... var failed = Enumerable.Range(1, 3000) .Select(i => new { arabic = i, roman = ToRoman(i) }) .Where(item => item.arabic != RomanToArabic(item.roman)) .Select(item => $"{item.roman} expected: {item.arabic} actual: {RomanToArabic(item.roman)}"); // No line should be printed out Console.Write(string.Join(Environment.NewLine, failed));

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