12. Integer to Roman (M)-优快云博客

本文介绍了一种将整数转换为罗马数字的方法，通过直接打表或减法策略，将整数1至3999转化为对应的罗马数字表示。文章提供了两种实现方式：一种是通过预设的罗马数字表来匹配每一位数字；另一种是通过递减的方式，从大到小匹配罗马数字符号。

Integer to Roman (M)

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.

题意

将整数转化为指定格式的罗马数字。

思路

直接打表，将每一位数字对应的罗马数字记录下来。
依次减去[1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1]，并转化为罗马数字添加到字符串中。

代码实现 - 打表

class Solution {
    public String intToRoman(int num) {
        String[] single = {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};
        String[] tens = {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};
        String[] hundreds = {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};
        String[] thousands = {"", "M", "MM", "MMM"};
        return thousands[num / 1000] + hundreds[(num % 1000) / 100] + tens[(num % 100) / 10] + single[num % 10];
    }
}

代码实现 - 减法

class Solution {
    public String intToRoman(int num) {
        String ans = "";
        int[] numeral = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
        String[] rome = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};
        for (int i = 0; i < numeral.length; i++) {
            int count = num / numeral[i];
            num -= count * numeral[i];
            while (count > 0) {
                ans += rome[i];
                count--;
            }
        }
        return ans;
    }
}