Roman to Integer

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Given a roman numeral, convert it to an integer.

Input is guaranteed to be within the range from 1 to 3999.

思路：

1.了解罗马字符与阿拉伯数字之间的关系；

String[] str = new String[] { "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I" };
int[] val = new int[] { 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 };

2.显然，数字数组是按大到小排列的，而且罗马字符也是按大到小排序且是唯一的；

3 遍历罗马字符数组，使用while循环将给定字符串从头开始与其匹配，看重叠部分是否完全一致，如果一致，则将结果加到sum上，并且将字符串已匹配的部分删除，重复此操作，直到数组遍历完成

 public int romanToInt(String s) {                String[] str = new String[] { "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I" };        int[] val = new int[] { 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 };                if(s==null) return 0;        int len=s.length();        if(len==0) return 0;                int sum=0;        for(int i=0;i<str.length;i++){                        while(s.length()>=str[i].length()&&str[i].equals(s.substring(0,str[i].length()))){                sum+=val[i];                s=s.substring(str[i].length());            }                    }                return sum;                    }

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