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:
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I can be placed before V (5) and X (10) to make 4 and 9.
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X can be placed before L (50) and C (100) to make 40 and 90.
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C can be placed before D (500) and M (1000) to make 400 and 900.
Given an integer, convert it to a roman numeral.
Example 1:
Input: num = 3
Output: “III”
Example 2:
Input: num = 4
Output: “IV”
Example 3:
Input: num = 9
Output: “IX”
Example 4:
Input: num = 58
Output: “LVIII”
Explanation: L = 50, V = 5, III = 《一线大厂Java面试题解析+后端开发学习笔记+最新架构讲解视频+实战项目源码讲义》无偿开源 威信搜索公众号【编程进阶路】 3.
Example 5:
Input: num = 1994
Output: “MCMXCIV”
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
Constraints:
- 1 <= num <= 3999
[](()Analysis
略
[](()Submission
public class IntegerToRoman {
// 方法一：我写的
public String intToRoman1(int num) {
if (num < 1 || num > 3999)
throw new IllegalArgumentException(String.valueOf(num));
StringBuilder sb = new StringBuilder();
int digit = 0;
while (num > 0) {
int n1 = num % 10;
if (n1 != 0) {
int n2 = n1 * (int) Math.pow(10, digit);
sb.insert(0, map(n2));
}
digit++;
num /= 10;
}
return sb.toString();
}
private String map(int num) {
if (0 < num && num <= 3)
return repeat(“I”, num);
if (num == 4)
return “IV”;
if (5 <= num && num <= 8)
return “V” + repeat(“I”, num - 5);
if (num == 9)
return “IX”;
if (10 <= num && num <= 30)
return repeat(“X”, num / 10);
if (num == 40)
return “XL”;
if (50 <= num && num <= 80)
return “L” + repeat(“X”, num / 10 - 5);
if (num == 90)
return “XC”;
if (100 <= num && num <= 300)
return repeat(“C”, num / 100);
if (num == 400)
return “CD”;
if (500 <= num && num <= 800)
return “D” + repeat(“C”, num / 100 - 5);
if (num == 900)
return “CM”;
if (1000 <= num && num <= 3000)
return repeat(“M”, num / 1000);
return “”;
}
private String repeat(String str, int num) {
if (num < 1)
return “”;
StringBuilder sb = new StringBuilder();
for (int i = 0; i < num; i++) {
sb.append(str);
}
return sb.toString();
}
// 方法二：挺巧妙的
public String intToRoman2(int num) {
int[] values = { 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 };
String[] strs = { “M”, “CM”, “D”, “CD”, “C”, “XC”, “L”, “XL”, “X”, “IX”, “V”, “IV”, “I” };
