12. Integer to Roman

题目：

Given an integer, convert it to a roman numeral.

Input is guaranteed to be within the range from 1 to 3999.

借鉴了别人的思路

知识点：罗马数字的表达，字符串合并

代码如下（C++）：

class Solution {
public:
    string intToRoman(int num) {
         //罗马数字的基本型为：I=1，V=5，X=10，L=50，C=100，D=500，M=1000，相同的罗马数字最多不能超过三个。所以对于4只能表示为5-1即IV，左减右加。
    //同理，9=IX，40=XL，90=XC，400=CD，900=CM。根据这些基本型，
       
    string thousand[4]={"","M","MM","MMM"};
    string hundred[11]={"","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"};
    string ten[11]={"","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"};
    string one[11]={"","I","II","III","IV","V","VI","VII","VIII","IX"};
    string result="";
    string* trans[4]={one,ten,hundred,thousand};
   
    int index=0;
    while(num!=0)
    {
        int key=num%10;
        result=trans[index][key]+result;   //加号前后的两个东西顺序不能变
        num=num/10;
        index++;
    }
   
    return result;
       
    }
};