Roman numerals are represented by seven different symbols: I
, V
, X
, L
, C
, D
and M
.
Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000
For example, two is written as II
in Roman numeral, just two one's added together. Twelve is written as, XII
, which is simply X
+ II
. The number twenty seven is written as XXVII
, which is XX
+ V
+ II
.
Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII
. Instead, the number four is written as IV
. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX
. There are six instances where subtraction is used:
-
I
can be placed beforeV
(5) andX
(10) to make 4 and 9. -
X
can be placed beforeL
(50) andC
(100) to make 40 and 90. -
C
can be placed beforeD
(500) andM
(1000) to make 400 and 900.
Given an integer, convert it to a roman numeral. Input is guaranteed to be within the range from 1 to 3999.
Example 1:
Input: 3 Output: "III"Example 2:
Input: 4 Output: "IV"Example 3:
Input: 9 Output: "IX"Example 4:
Input: 58 Output: "LVIII" Explanation: L = 50, V = 5, III = 3.Example 5:
Input: 1994 Output: "MCMXCIV" Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
整数转换罗马数字。
13题是正好相反。题意是给一个整数,请把它转换成罗马数字。
这个题不涉及什么算法或者思想,只是单纯的转换。我给出一个我个人觉得比较好记的做法。先给出每个罗马数字和他们对应的整数之间的mapping,然后对于要处理的整数X,找到最大的小于X的对应的罗马数字。因为是JavaScript,所以这里可以直接拼接字符串而不用像Java那样先创建StringBuilder(12行)。
时间O(n)
空间O(n)
JavaScript实现
1 /** 2 * @param {number} num 3 * @return {string} 4 */ 5 var intToRoman = function (num) { 6 var list = ['M', 'CM', 'D', 'CD', 'C', 'XC', 'L', 'XL', 'X', 'IX', 'V', 'IV', 'I']; 7 var valueList = [1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1]; 8 var res = ''; 9 while (num !== 0) { 10 for (var i = 0; i < valueList.length; i++) { 11 if (num >= valueList[i]) { 12 res += list[i]; 13 num -= valueList[i]; 14 break; 15 } 16 } 17 } 18 return res; 19 };
Java实现
1 class Solution { 2 public String intToRoman(int num) { 3 int[] values = {1000,900,500,400,100,90,50,40,10,9,5,4,1}; 4 String[] strs = {"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"}; 5 6 StringBuilder sb = new StringBuilder(); 7 8 for (int i = 0; i < values.length; i++) { 9 while (num >= values[i]) { 10 num -= values[i]; 11 sb.append(strs[i]); 12 } 13 } 14 return sb.toString(); 15 } 16 }