Leet Code 13.罗马数字转整数

与12题一样的规则，将罗马数字转为整数。

思路

字符串str从左到右遍历，不断将一个长度和两个长度的子字符串与罗马字符匹配，匹配成功就将数值相加

import java.util.*;

import static java.lang.Math.min;

public class leetcode {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String str = scan.nextLine();
        int num = romanToInt(str);
        System.out.println(num);
    }

    public static int romanToInt(String s) {
        //初始化
        int[] Roman_num = {1,4,5,9,10,40,50,90,100,400,500,900,1000};
        String[] Roman_str = {"I","IV","V","IX","X","XL","L","XC","C","CD","D","CM","M"};

        int num = 0,index=12;
        boolean equal = false;
        for(int i = 0; i<s.length(); ) {
            equal =false;
            if(s.substring(i,i+1).equals(Roman_str[index])) {
                num += Roman_num[index];
                i++;
                equal = true;
            }
            else if(s.substring(i).length() >= 2 && s.substring(i,i+2).equals(Roman_str[index])) {
                num += Roman_num[index];
                i += 2;
                equal = true;
            }
            if(equal == false) index--;
        }
        return num;
    }
}

小结

忘记了String相等不能用==，以至于索引报错，一直在想索引怎么会出错。要注意substring的索引不能超出边界，可以求长度来避免这个情况。