十进制与罗马数字互转

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import java.util.HashMap;
import java.util.Map;

/**
 * 罗马数字与十进制计算工具
 *
 * @author maxzhao
 * @since 2022-12-19 09:29
 */
public class RomanSerialNumberUtil {
    /**
     * 罗马数字对应的十进制
     */
    private static final Map<String, Integer> ROMAN_SERIAL_NUMBER_MAP;
    /**
     * 数字间隔计算，从大到小
     */
    private static final int[] DIGITS = new int[13];
    /**
     * 数字对应小写的罗马数字
     */
    private static final Map<Integer, String> NUM_TO_LOWER_ROMAN_SERIAL_NUMBER = new HashMap<>();
    /**
     * 数字对应大写的罗马数字
     */
    private static final Map<Integer, String> NUM_TO_UPPER_ROMAN_SERIAL_NUMBER = new HashMap<>();

    static {
        ROMAN_SERIAL_NUMBER_MAP = new HashMap<>(32);
        ROMAN_SERIAL_NUMBER_MAP.put("I", 1);
        ROMAN_SERIAL_NUMBER_MAP.put("i", 1);
        ROMAN_SERIAL_NUMBER_MAP.put("V", 5);
        ROMAN_SERIAL_NUMBER_MAP.put("v", 5);
        ROMAN_SERIAL_NUMBER_MAP.put("X", 10);
        ROMAN_SERIAL_NUMBER_MAP.put("x", 10);
        ROMAN_SERIAL_NUMBER_MAP.put("L", 50);
        ROMAN_SERIAL_NUMBER_MAP.put("l", 50);
        ROMAN_SERIAL_NUMBER_MAP.put("C", 100);
        ROMAN_SERIAL_NUMBER_MAP.put("c", 100);
        ROMAN_SERIAL_NUMBER_MAP.put("D", 500);
        ROMAN_SERIAL_NUMBER_MAP.put("d", 500);
        ROMAN_SERIAL_NUMBER_MAP.put("M", 1000);
        ROMAN_SERIAL_NUMBER_MAP.put("m", 1000);
        ROMAN_SERIAL_NUMBER_MAP.put("IV", 4);
        ROMAN_SERIAL_NUMBER_MAP.put("iv", 4);
        ROMAN_SERIAL_NUMBER_MAP.put("IX", 9);
        ROMAN_SERIAL_NUMBER_MAP.put("ix", 9);
        ROMAN_SERIAL_NUMBER_MAP.put("XL", 40);
        ROMAN_SERIAL_NUMBER_MAP.put("xl", 40);
        ROMAN_SERIAL_NUMBER_MAP.put("XC", 90);
        ROMAN_SERIAL_NUMBER_MAP.put("xc", 90);
        ROMAN_SERIAL_NUMBER_MAP.put("CD", 400);
        ROMAN_SERIAL_NUMBER_MAP.put("cd", 400);
        ROMAN_SERIAL_NUMBER_MAP.put("CM", 900);
        ROMAN_SERIAL_NUMBER_MAP.put("cm", 900);
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(1, "i");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(5, "v");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(10, "x");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(50, "l");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(100, "c");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(500, "d");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(1000, "m");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(4, "iv");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(9, "ix");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(40, "xl");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(90, "xc");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(400, "cd");
        NUM_TO_LOWER_ROMAN_SERIAL_NUMBER.put(900, "cm");


        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(1, "I");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(5, "V");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(10, "X");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(50, "L");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(100, "C");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(500, "D");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(1000, "M");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(4, "IV");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(9, "IX");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(40, "XL");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(90, "XC");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(400, "CD");
        NUM_TO_UPPER_ROMAN_SERIAL_NUMBER.put(900, "CM");

        DIGITS[0] = 1000;
        DIGITS[1] = 900;
        DIGITS[2] = 500;
        DIGITS[3] = 400;
        DIGITS[4] = 100;
        DIGITS[5] = 90;
        DIGITS[6] = 50;
        DIGITS[7] = 40;
        DIGITS[8] = 10;
        DIGITS[9] = 9;
        DIGITS[10] = 5;
        DIGITS[11] = 4;
        DIGITS[12] = 1;
    }

    /**
     * 数字转小写罗马字符串
     *
     * @param num 字符串
     * @return 数字
     */
    public static String toLowerRomanSerialNumber(int num) {
        return toRomanSerialNumber(num, true);
    }
    /**
     * 数字转大写罗马字符串
     *
     * @param num 字符串
     * @return 数字
     */
    public static String toUpperRomanSerialNumber(int num) {
        return toRomanSerialNumber(num, false);
    }
    /**
     * 数字转罗马字符串
     *
     * @param num 字符串
     * @return 数字
     */
    public static String toRomanSerialNumber(int num,boolean lowerChar) {
        Map<Integer, String> chars = lowerChar ? NUM_TO_LOWER_ROMAN_SERIAL_NUMBER : NUM_TO_UPPER_ROMAN_SERIAL_NUMBER;
        String res = "";
        while (num > 0) {
            for (int digit : DIGITS) {
                if (num >= digit) {
                    res += chars.get(digit);
                    num -= digit;
                    break;
                }
            }
        }
        return res;
    }

    /**
     * 罗马字符串转 数字
     *
     * @param roman 字符串
     * @return 数字
     */
    public static int getLowerRomanSerialNumber(String roman) {
        int res = 0;
        int idx = 0;
        while (idx < roman.length()) {
            if (idx + 1 < roman.length() && ROMAN_SERIAL_NUMBER_MAP.containsKey(roman.substring(idx, idx + 2))) {
                res += ROMAN_SERIAL_NUMBER_MAP.get(roman.substring(idx, idx + 2));
                idx += 2;
            } else {
                res += ROMAN_SERIAL_NUMBER_MAP.get(roman.substring(idx, idx + 1));
                idx++;
            }

        }
        return res;
    }
}

本文地址： https://github.com/maxzhao-it/blog/post/b87a95cb/