# JavaScript Algorithms: Roman to Integer (LeetCode)

--

# Description

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

, `V`

, `X`

, `L`

, `C`

, `D`

and `M`

.

**Symbol** **Value**

I 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:** 58

**Explanation:** L = 50, V= 5, III = 3.

**Example 5:**

**Input:** "MCMXCIV"

**Output:** 1994

**Explanation:** M = 1000, CM = 900, XC = 90 and IV = 4.

# Solution

First of all, need to create a Map with Roman-Integer key-value pairs. After that, we can loop through the string and count the result variable.

## The problem with IX, IV, XC …

We need to figure out how we can count these Roman values.

The rule is pretty simple — if the next value is bigger than the current, we need to subtract the current value from the next. For example:

So. inside the for loop we’re going to create a *current* and *next* variable. And depending on whether the *next* is bigger than the *current*, we’re filling the result:

Thanks for reading! Looking forward to your feedback. See you soon ✌️