LeetCode 12. Integer to Roman

题目要求:

Given an integer, convert it to a roman numeral.

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

关于罗马数字的表示方法参考这里https://www.wikiwand.com/en/Roman_numerals

Symbol	Value
I	1
V	5
X	10
L	50
C	100
D	500
M	1000

同时有以下三条规则:

• I placed before V or X indicates one less, so four is IV (one less than five) and nine is IX (one less than ten)
• X placed before L or C indicates ten less, so forty is XL (ten less than fifty) and ninety is XC (ten less than a hundred)
• C placed before D or M indicates a hundred less, so four hundred is CD (a hundred less than five hundred) and nine hundred is CM (a hundred less than a thousand)

整数转化为罗马数字，简单模拟。

class Solution {
public:
    string intToRoman(int num) {
        int numArr[4] = {0};
        int numArrIndex = 3;
        while(num > 0){
            numArr[numArrIndex--] = num % 10;
            num /= 10;
        }
        string ret;

        for(int i = 3, offset = 1; i >= 0; i--, offset *= 10){
            if(numArr[i] == 0) continue;
            else if(numArr[i] < 4){
                for(int j = 0; j < numArr[i]; j++) ret.push_back(valToSymbol(1 * offset));
            }
            else if(numArr[i] == 4){
                ret.push_back(valToSymbol(5 * offset));
                ret.push_back(valToSymbol(1 * offset));
            }
            else if(numArr[i] < 9){
                for(int j = 5; j < numArr[i]; j++) ret.push_back(valToSymbol(1 * offset));
                ret.push_back(valToSymbol(5 * offset));
            }
            else{
                ret.push_back(valToSymbol(10 * offset));
                ret.push_back(valToSymbol(1 * offset));
            }
        }
        reverse(ret.begin(), ret.end());
        return ret;
    }
    
    char valToSymbol(int val){
        switch(val){
            case 1:
                return 'I';
            case 5:
                return 'V';
            case 10:
                return 'X';
            case 50:
                return 'L';
            case 100:
                return 'C';
            case 500:
                return 'D';
            case 1000:
                return 'M';
            default:
                return 0;
        }
    }
};

Runtime: 28ms