Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.
Examples:
Input: "III"
Output: 3
Input: "IV"
Output: 4
Input: "IX"
Output: 9
Input: "LVIII"
Output: 58
Explanation: L = 50, V= 5, III = 3.
Input: "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
Thoughts
- 首先使用一个函数来转换每个罗马字符对应的数字
- 然后利用罗马数字表示法的特性，如果当前字母对应的数值比后面的大，则要加上当前的数值，否则则要减去当前的数值
- 遍历字符串，加减得到最后结果
\(M(1000)C(-100)M(1000)X(-10)C(100)I(-1)V(5) \tag{1}\) \(1000 - 100 + 1000 - 10 + 100 - 1 + 5 = 1994 \tag{2}\) \(MCMXCIV = 1994 \tag{3}\)
Code(JAVA)
public int romanToInt(String s) {
int res = 0;
int prev = getValue(s.charAt(0));
for(int i = 1; i < s.length(); i++) {
int cur = getValue(s.charAt(i));
if(prev < cur)
res -= prev;
else
res += prev;
prev = cur;
}
return res + prev;
}
private int getValue(char c){
switch(c) {
case 'I':return 1;
case 'V':return 5;
case 'X':return 10;
case 'L':return 50;
case 'C':return 100;
case 'D':return 500;
case 'M':return 1000;
default: return 0;
}
}
