Roman numerals are represented by seven different symbols: `I`

, `V`

, `X`

, `L`

, `C`

, `D`

and `M`

.

SymbolValueI 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`

, 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.

**Example 1:**

Input:"III"Output:3

**Example 2:**

Input:"IV"Output:4

**Example 3:**

Input:"IX"Output:9

**Example 4:**

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

**Example 5:**

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

## Submission

My submission is like solving a regular expression problem.

class Solution { public int romanToInt(String s) { Map<String, Integer> map = Map.of("I", 1, "V", 5, "X", 10, "L", 50, "C", 100, "D", 500, "M", 1000); if(s.length() == 0) { return 0; } if(s.length() == 1) { return(map.get(s.substring(0, 1))); } String sub2 = s.substring(0, 2); if(sub2.compareTo("IV") == 0) { return 4 + romanToInt(s.substring(2)); } if(sub2.compareTo("IX") == 0) { return 9 + romanToInt(s.substring(2)); } if(sub2.compareTo("XL") == 0) { return 40 + romanToInt(s.substring(2)); } if(sub2.compareTo("XC") == 0) { return 90 + romanToInt(s.substring(2)); } if(sub2.compareTo("CD") == 0) { return 400 + romanToInt(s.substring(2)); } if(sub2.compareTo("CM") == 0) { return 900 + romanToInt(s.substring(2)); } return map.get(s.substring(0, 1)) + romanToInt(s.substring(1)); } }