# 13. Roman to Integer

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.

class Solution { /** * @param String $s * @return Integer */ function romanToInt($s) { $i= 0; $p = ["I"=>1, "V"=>5, "X"=>10, "L"=>50, "C"=> 100, "D"=>500, "M"=>1000]; $result = 0; $increment = INF; while($i < strlen($s)){ $new_increment = $p[$s[$i]]; if($increment < $new_increment){ $result -= (2 * $increment); } $increment = $new_increment; $result += $increment; $i ++; } return $result; } }

The solution is based on the fact that the input is valid, otherwise won’t work

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