Given an integer, convert it to a roman numeral.
Input is guaranteed to be within the range from 1 to 3999.
Solution:
以3999，为例：
class Solution {
public:
string intToRoman(int num) {
if(num<1||num>3999) return NULL;
string str;
while(num){
if(num/1000!=0){
for(int i=0;i<num/1000;i++) str+="M";
num=num%1000;
}else if(num/100!=0){
int tmp=num/100;
if(tmp%5==4){
if(tmp/5==0){
str+="C";str+="D";
}else{
str+="C";str+="M";
}
}else{
if(tmp/5!=0){
str+="D";
}
for(int i=0;i<tmp%5;i++) str+="C";
}
num=num%100;
}else if(num/10!=0){
int tmp=num/10;
if(tmp%5==4){
if(tmp/5==0){
str+="X";str+="L";
}else{
str+="X";str+="C";
}
}else{
if(tmp/5!=0){
str+="L";
}
for(int i=0;i<tmp%5;i++) str+="X";
}
num=num%10;
}else{
if(num%5==4){
if(num/5==0){
str+="I";str+="V";
}else{
str+="I";str+="X";
}
}else{
if(num/5!=0){
str+="V";
}
for(int i=0;i<num%5;i++) str+="I";
}
num=num%1;
}
}
return str;
}
};