【LeetCode】12. Integer to Roman - Java实现

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1. 题目描述：

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.

2. 思路分析：

题目的意思是将普通int转成罗马数字，并且题目给出了罗马数字的表示方式。

其中每两个阶段的之间有一个减法的表示，比如900=CM， C写在M前面表示M-C。

题目的范围给到3999，感觉情况不多直接打表其实更快。

3. Java代码：

源代码：见我GiHub主页

代码：

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