# 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:

``````Input: 3
Output: "III"
``````

Example 2:

``````Input: 4
Output: "IV"
``````

Example 3:

``````Input: 9
Output: "IX"
``````

Example 4:

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

Example 5:

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

Constraints:

• `1 <= num <= 3999`

I - 1

V - 5

X - 10

L - 50

C - 100

D - 500

M - 1000

100 - C

200 - CC

300 - CCC

400 - CD

500 - D

600 - DC

700 - DCC

800 - DCCC

900 - CM

``````class Solution {
public:
string intToRoman(int num) {
string res = "";
vector<char> roman{'M', 'D', 'C', 'L', 'X', 'V', 'I'};
vector<int> value{1000, 500, 100, 50, 10, 5, 1};
for (int n = 0; n < 7; n += 2) {
int x = num / value[n];
if (x < 4) {
for (int i = 1; i <= x; ++i) res += roman[n];
} else if (x == 4) {
res = res + roman[n] + roman[n - 1];
} else if (x > 4 && x < 9) {
res += roman[n - 1];
for (int i = 6; i <= x; ++i) res += roman[n];
} else if (x == 9) {
res = res + roman[n] + roman[n - 2];
}
num %= value[n];
}
return res;
}
};
``````

``````class Solution {
public:
string intToRoman(int num) {
string res = "";
vector<int> val{1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
vector<string> str{"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};
for (int i = 0; i < val.size(); ++i) {
while (num >= val[i]) {
num -= val[i];
res += str[i];
}
}
return res;
}
};
``````

``````class Solution {
public:
string intToRoman(int num) {
string res = "";
vector<string> v1{"", "M", "MM", "MMM"};
vector<string> v2{"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};
vector<string> v3{"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};
vector<string> v4{"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};
return v1[num / 1000] + v2[(num % 1000) / 100] + v3[(num % 100) / 10] + v4[num % 10];
}
};
``````

Github 同步地址：

https://github.com/grandyang/leetcode/issues/12

Roman to Integer

Integer to English Words

https://leetcode.com/problems/integer-to-roman/

https://leetcode.com/problems/integer-to-roman/discuss/6274/simple-solution

https://leetcode.com/problems/integer-to-roman/discuss/6310/my-java-solution-easy-to-understand

LeetCode All in One 题目讲解汇总(持续更新中…)

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