文章目錄

• 1. 題目描述：
• 2. 思路分析：
• 3. Java程式碼：

1. 題目描述：

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

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

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

Example 1:

Input: “III”
Output: 3

Example 2:

Input: “IV”
Output: 4

Example 3:

Input: “IX”
Output: 9

Example 4:

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

Example 5:

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

2. 思路分析：

題目的意思是將羅馬數字轉成普通int，並且題目給出了羅馬數字的表示方式。

思路就是遍歷羅馬字母，如果當前的羅馬字母表示的數字比右邊的大，則直接累加即可，如果比右邊的小，則需要減去當前羅馬字母表示的數字。

3. Java程式碼：

原始碼：見我GiHub主頁

程式碼：

public static int romanToInt(String s) {
    Map<Character, Integer> romanMap = new HashMap<>();
    romanMap.put('I', 1);
    romanMap.put('V', 5);
    romanMap.put('X', 10);
    romanMap.put('L', 50);
    romanMap.put('C', 100);
    romanMap.put('D', 500);
    romanMap.put('M', 1000);
    int result = 0;
    for (int i = 0; i < s.length(); i++) {
        if (i == s.length() - 1 || romanMap.get(s.charAt(i)) >= romanMap.get(s.charAt(i + 1))) {
            result += romanMap.get(s.charAt(i));
        } else {
            result -= romanMap.get(s.charAt(i));
        }
    }
    return result;
}