Leetcode 12 Integer To Roman

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

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

For example, two is written as II in Roman numeral, just two one’s added together. Twelve is written as, XII, which is simply X + II. The number twenty seven is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

I can be placed before V (5) and X (10) to make 4 and 9.
X can be placed before L (50) and C (100) to make 40 and 90.
C can be placed before D (500) and M (1000) to make 400 and 900.

Given an integer, convert it to a roman numeral. Input is guaranteed to be within the range from 1 to 3999.

Example 1:

1 2	Input: 3 Output: "III"

Example 2:

1 2	Input: 4 Output: "IV"

Example 3:

1 2	Input: 9 Output: "IX"

Example 4:

1
2
3

Input: 58
Output: "LVIII"
Explanation: L = 50, V = 5, III = 3.

Example 5:

1
2
3

Input: 1994
Output: "MCMXCIV"
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

1 🧠短路的做法

至今仍然想不明白为什么我不用数组存储这个映射, 而是用hashmap…… 代码又慢又长…或许需要重新new一个🧠了

class Solution {
public:
    string intToRoman(int num) {
        int one = num % 10;
        int ten = (num / 10) % 10;
        int hundred = (num / 100) % 10;
        int thousand = (num / 1000) % 10;
        return thousandDigit[thousand] + hundredDigit[hundred] + tenDigit[ten] + oneDigit[one];
    }
    Solution()
    {
        init();
    }
private:
    unordered_map<int, string> thousandDigit;
    unordered_map<int, string> hundredDigit;
    unordered_map<int, string> tenDigit;
    unordered_map<int, string> oneDigit;
    void init()
    {
        thousandDigit.insert({0,""});
        thousandDigit.insert({1,"M"});
        thousandDigit.insert({2,"MM"});
        thousandDigit.insert({3,"MMM"});
        hundredDigit.insert({0,""});
        hundredDigit.insert({1,"C"});
        hundredDigit.insert({2,"CC"});
        hundredDigit.insert({3,"CCC"});
        hundredDigit.insert({4,"CD"});
        hundredDigit.insert({5,"D"});
        hundredDigit.insert({6,"DC"});
        hundredDigit.insert({7,"DCC"});
        hundredDigit.insert({8,"DCCC"});
        hundredDigit.insert({9,"CM"});
        tenDigit.insert({0,""});
        tenDigit.insert({1,"X"});
        tenDigit.insert({2,"XX"});
        tenDigit.insert({3,"XXX"});
        tenDigit.insert({4,"XL"});
        tenDigit.insert({5,"L"});
        tenDigit.insert({6,"LX"});
        tenDigit.insert({7,"LXX"});
        tenDigit.insert({8,"LXXX"});
        tenDigit.insert({9,"XC"});
        oneDigit.insert({0,""});
        oneDigit.insert({1,"I"});
        oneDigit.insert({2,"II"});
        oneDigit.insert({3,"III"});
        oneDigit.insert({4,"IV"});
        oneDigit.insert({5,"V"});
        oneDigit.insert({6,"VI"});
        oneDigit.insert({7,"VII"});
        oneDigit.insert({8,"VIII"});
        oneDigit.insert({9,"IX"});
    }
};

2 正确做法

class Solution {
public:
    string intToRoman(int num) {
        int one = num % 10;
        int ten = (num / 10) % 10;
        int hundred = (num / 100) % 10;
        int thousand = (num / 1000) % 10;
        return thousandDigit[thousand] + hundredDigit[hundred] + tenDigit[ten] + oneDigit[one];
    }
private:
    string thousandDigit[4] = {"", "M", "MM", "MMM"};
    string hundredDigit[10] = {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};
    string tenDigit[10] = {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};
    string oneDigit[10] = {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};
};