LeetCode - Integer to Roman

LeetCode - Integer to Roman

2013.12.1 22:56

Given an integer, convert it to a roman numeral.

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

Solution:

　　First of all, for those who lacks background knowledge of Roman numerals(including me), here is the wiki:

　　　　http://en.wikipedia.org/wiki/Roman_numerals

　　My solution is to get the result from the most significant digit to the lowest. The representation of each digit can be pre-defined and stored in a dictionary. We'll just concatenate the Roman representation for each digit to get the final result.

　　Time complexity is O(lg(n)), where n is the input integer. Space complexity is O(lg(n)), actually 10 * lg(n).

Accepted code:

//1CE, 1RE, 1WA, 1AC
class Solution {
public:
    string intToRoman(int num) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.    
        string res;
        int a[4];
        
        a[0] = num % 10;
        num /= 10;
        a[1] = num % 10;
        num /= 10;
        a[2] = num % 10;
        num /= 10;
        a[3] = num % 10;
        num /= 10;
        
        res = "";
        //2WA here..
        /*
        for(int i = 0; i < 4; ++i){
            res += code[i][a[i]];
        }
        */
        /*
        for(int i = 3; i >= 0; ++i){
            res += code[i][a[i]];
        }
        */
        for(int i = 3; i >= 0; --i){
            res += code[i][a[i]];
        }
        
        return res;
    }
private:
    const string code[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", "", "", "", "", "", ""}
    };
};