LeetCode刷题day014 (Jieky)

LeetCode第13题

/*
Roman numerals are represented by seven different symbols: I(1), V(5), X(10), L(50), C(100), D(500) and M(1000).

For example, two is written as II in Roman numeral, just two one's added together. Twelve is writen 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 a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.

*/
import java.util.*;
public class RomanToInteger{
     
	public static void main(String[] args){
     
		RomanToInteger rti = new RomanToInteger();
		int result = rti.romanToInt("XIV");;
		System.out.println(result);
	}
	
	//罗马数字转阿拉伯数字。特殊情况4,9,40,90,400,900，
	public int romanToInt(String s) {
     
		if(s == null || s.equals("")) return 0;
		
		Character[] romanArray = {
     'I','V','X','L','C','D','M'};
		int[] alaboArray = {
     1,5,10,50,100,500,1000};
		
		// public static  List asList(T... a) {
     
			// return new ArrayList<>(a);
		// }
		// ArrayList 有序，可重复
		List<Character> romanList = Arrays.asList(romanArray);
		
		int ret = 0;
		
		// ArrayList.indexOf() 获得元素索引
		int pre = romanList.indexOf(s.charAt(0));
		for(int i = 1;i < s.length();i++){
     
			int cur = romanList.indexOf(s.charAt(i));
			
			// 根据罗马数字书写规律，一个大的数前面连续最多一个数比他小
			if (alaboArray[pre] < alaboArray[cur]){
     
				ret -= alaboArray[pre];
			}else{
     
				ret += alaboArray[pre];
			}
			pre = cur;
		}
        // 加上最后一位罗马数字，记得处理好最后一位罗马字符，特殊情况是只有一位的罗马数字
		ret += alaboArray[pre];
		return ret;
	}
}