Integer to Roman & Roman to Integer

Integer to Roman

Given an integer, convert it to a roman numeral.

The number is guaranteed to be within the range from 1 to 3999.

Clarification

What is Roman Numeral?

• https://en.wikipedia.org/wiki/Roman_numerals
• https://zh.wikipedia.org/wiki/%E7%BD%97%E9%A9%AC%E6%95%B0%E5%AD%97
• http://baike.baidu.com/view/42061.htm

Example

4 -> IV

12 -> XII

21 -> XXI

99 -> XCIX

more examples at: http://literacy.kent.edu/Minigrants/Cinci/romanchart.htm

分析：

在罗马数字里，除了1000, 900, 500, 400, 100,90, 50, 40, 10, 9, 5, 4, 1 ，其它数字都可以由以上数字“拼接”而成。以上数字的罗马字符为：

"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I" 。

所以，对于15，我们找出10和5，放在一起就是XV，16就是10+5+1， XVI（这里一定是从大到小，能够取最大就必须取最大，不能是 10 + 4 + 1 + 1）.

 public class Solution {
     /**
      * @param n
      *            The integer
      * @return Roman representation
      */

     public String intToRoman(int number) {
         int[] values = { , , , , , , , , , , , ,  };
         String[] numerals = { "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I" };
         StringBuilder result = new StringBuilder();
         for (int i = ; i < values.length; i++) {
             while (number >= values[i]) {
                 number -= values[i];
                 result.append(numerals[i]);
             }
         }
         return result.toString();
     }
 }

Roman to Integer

Given a roman numeral, convert it to an integer.

The answer is guaranteed to be within the range from 1 to 3999.

Clarification

What is Roman Numeral?

• https://en.wikipedia.org/wiki/Roman_numerals
• https://zh.wikipedia.org/wiki/%E7%BD%97%E9%A9%AC%E6%95%B0%E5%AD%97
• http://baike.baidu.com/view/42061.htm

Example

IV -> 4

XII -> 12

XXI -> 21

XCIX -> 99

 public class Solution {
     /**
      * @param s Roman representation
      * @return an integer
      */
     public int romanToInt(String s) {
         if(s.length() < ) return ;
         int value = ;
         int pValue = getRomanValue(s.charAt()); // the value of previous character

         for (int i = ; i < s.length(); i++) {
             int cValue = getRomanValue(s.charAt(i));
             if (pValue >= cValue) {
                 value += pValue;
             } else {
                 value -= pValue;
             }
             pValue = cValue;
         }
         value += pValue; // we always add the last value to value. No exception.
         return value;

     }
     public int getRomanValue(char c) {
         switch(c) {
             case 'I': return ;
             case 'V': return ;
             case 'X': return ;
             case 'L': return ;
             case 'C': return ;
             case 'D': return ;
             case 'M': return ;
             default: return ;
         }
     }
 }