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）.

 1 public class Solution {
 2     /**
 3      * @param n
 4      *            The integer
 5      * @return Roman representation
 6      */
 7
 8     public String intToRoman(int number) {
 9         int[] values = { 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 };
10         String[] numerals = { "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I" };
11         StringBuilder result = new StringBuilder();
12         for (int i = 0; i < values.length; i++) {
13             while (number >= values[i]) {
14                 number -= values[i];
15                 result.append(numerals[i]);
16             }
17         }
18         return result.toString();
19     }
20 }

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

 1 public class Solution {
 2     /**
 3      * @param s Roman representation
 4      * @return an integer
 5      */
 6     public int romanToInt(String s) {
 7         if(s.length() < 1) return 0;
 8         int value = 0;
 9         int pValue = getRomanValue(s.charAt(0)); // the value of previous character
10
11         for (int i = 1; i < s.length(); i++) {
12             int cValue = getRomanValue(s.charAt(i));
13             if (pValue >= cValue) {
14                 value += pValue;
15             } else {
16                 value -= pValue;
17             }
18             pValue = cValue;
19         }
20         value += pValue; // we always add the last value to value. No exception.
21         return value;
22
23     }
24     public int getRomanValue(char c) {
25         switch(c) {
26             case ‘I‘: return 1;
27             case ‘V‘: return 5;
28             case ‘X‘: return 10;
29             case ‘L‘: return 50;
30             case ‘C‘: return 100;
31             case ‘D‘: return 500;
32             case ‘M‘: return 1000;
33             default: return 0;
34         }
35     }
36 }