Java程序：将1到3999之间的罗马数字转换为十进制

import java.util.*;

// Create a class for initializing the function to return the Roman symbol's value.
public class Solution{
   // This function is created to return a Roman symbol's value.
   int romanValue(char ch)    {
      if(ch=='I')
         return 1;
      else if(ch=='V')
         return 5;
      else if(ch=='X')
         return 10;
      else if(ch=='L')
         return 50;
      else if(ch=='C')
         return 100;
      else if(ch=='D')
         return 500;
      else if(ch=='M')
         return 1000;
      return -1;
   } 
   
   // This function is created for the conversion of Roman numerals to decimal numerals
   int convertRomanToDecimal(String str) {
      // Initialize decimal value 
      int decVal = 0;
      int n = str.length(); // Getting the size of the string
      for (int i = 0; i < n; i++) {
         // check if i+1 charchter exist and getting value of roman symbol str[i] and str[i+1]
         if (i + 1 < n && romanValue(str.charAt(i)) < romanValue(str.charAt(i + 1)))  {
            //subtract the current value from the next value and add the decVal variable
            decVal = decVal + romanValue(str.charAt(i + 1)) - romanValue(str.charAt(i));
            i++; // Increment the index of the string to point to the next char
         }
         // If i+1 char not exist
         else {
            decVal = decVal + romanValue(str.charAt(i)); // add the first char value
         }
      } 
      return decVal; // Return decimal value
   } 
   public static void main(String args[]) {
      Solution ob = new Solution(); 
      String str = "MCMIX"; // Given string
      System.out.println("Roman Numeral: " + str);
      // Print the decimal form and call the function of conversion
      System.out.println("The decimal Numeral form of the Roman Numeral" + " is " + ob.convertRomanToDecimal(str));
   }
}

import java.util.Map;
import java.util.HashMap;
public class Solution {
   public static final Map<Character,
      Integer> romanValue = new HashMap<Character,
   Integer>() {
      {
         put ( 'M', 1000 );
         put ( 'D', 500 );
         put ( 'C', 100 );
         put ( 'L', 50 );
         put ( 'X', 10 );
         put ( 'V', 5 );
         put ( 'I', 1 );
      }
   };
   // Function is created for conversion of the Roman numeral to decimal numeral
   private static int convertRomanToDecimal(String str) {
      // Initialize decimal value
      int decVal = 0;
      for (int i = 0; i < str.length(); i++) {
         // store numeric value of roman symbol str[i]
         int first = romanValue.get(str.charAt(i));
         // check if i+1 charchter exist or not
         if (i + 1 < str.length()) {
            // store numeric value of roman symbol str[i+1]
            int second = romanValue.get(str.charAt(i + 1));
            // check which value is greater first or second
            if (first <= second) {
               // if first value <= second add first value to variable decVal
               decVal = decVal + first;
            } else  {
               // Value of first char is less than to the the second char
               decVal = decVal + second - first;
               i++; // Increment the index of string to point to next char
            }
         }
         // If i+1 char not exist
         else {
            decVal = decVal + first; // add the first char value
         }
      }
      return decVal; // Return decimal value
   }
   public static void main(String args[]) {
      String str = "MMMIX"; // Given string
      System.out.println("Roman Numeral: " + str);
      // print the decimal form and call function of conversion
      System.out.println("Decimal Numeral form of Roman Numeral" +
         " is " + convertRomanToDecimal(str));
    }
}