Leecode #12 Integer to Roman

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本文详细解析了LeetCode第12题的解决方案，该题要求将整数转换为罗马数字表示。文章介绍了罗马数字的基本构成和特殊规则，如IV代表4，IX代表9等，并提供了一段C++代码实现，通过构建四维数组来匹配不同的数值范围，最终完成转换。

一、问题描述
Leecode第十二题，题目为：
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 before V (5) and X (10) to make 4 and 9.
X can be placed before L (50) and C (100) to make 40 and 90.
C can be placed before D (500) and M (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.

问题理解为：

二、解题思路

三、实现代码

class Solution {
public:
    string intToRoman(int num) {
        string c[4][10]={
            {"","I","II","III","IV","V","VI","VII","VIII","IX"},
            {"","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"},
            {"","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"},
            {"","M","MM","MMM"}};
        string roman_data;
        roman_data.append(c[3][num / 1000 % 10]);
        roman_data.append(c[2][num / 100 % 10]);
        roman_data.append(c[1][num / 10 % 10]);
        roman_data.append(c[0][num % 10]);
         
        return roman_data;
    }
};


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