12. Integer to Roman

1.問題

2.想法

• 提問

• function header, parameter

• test input

• 說明想法

  • 用ordered_map儲存個, 十, 百, 位數

  • 針對個, 十, 百, 位數mapping到對應的值

• 測試計算複雜度: O(n)

3.程式碼

class Solution {
public:
    string intToRoman(int num) {
        unordered_map <int, string>m;
        string s = "";
        m[1] = "I";
        m[2] = "II";
        m[3] = "III";
        m[4] = "IV";
        m[5] = "V";
        m[6] = "VI";
        m[7] = "VII";
        m[8] = "VIII";
        m[9] = "IX";
        m[10] = "X";
        m[20] = "XX";
        m[30] = "XXX";
        m[40] = "XL";
        m[50] = "L";
        m[60] = "LX";
        m[70] = "LXX";
        m[80] = "LXXX";
        m[90] = "XC";
        m[100] = "C";
        m[200] = "CC";
        m[300] = "CCC";
        m[400] = "CD";
        m[500] = "D";
        m[600] = "DC";
        m[700] = "DCC";
        m[800] = "DCCC";
        m[900] = "CM";
        m[1000] = "M";
        m[2000] = "MM";
        m[3000] = "MMM";
        int i = 0;
        while (num > 0) {
            int n = num % 10;
            s = m[n * int(pow(10, i))] + s;
            i ++;
            num = num / 10;
        }
        return s;
    }
};