Roman numerals are represented by seven different symbols:

Symbol Value

I 1

V 5

X 10

L 50

C 100

D 500

M 1000

For example, 2 is written as II in Roman numeral, just two ones added together. 12 is written as XII, which is simply X + II. The number 27 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.

To convert a Roman numeral to an integer in PHP, you can create a function that iterates through the Roman numeral string and adds the corresponding values to a running total. You’ll need to consider the rules for Roman numerals, such as the cases where subtraction is used.

Here’s a PHP function to convert a Roman numeral to an integer:

class Solution { /** * @param String $s * @return Integer */ function romanToInt($s) { $romanValues = [ 'I' => 1, 'V' => 5, 'X' => 10, 'L' => 50, 'C' => 100, 'D' => 500, 'M' => 1000, ]; $total = 0; $prevValue = 0; // Loop through the Roman numeral string in reverse order for ($i = strlen($s) - 1; $i >= 0; $i--) { $currentValue = $romanValues[$s[$i]]; // If the current value is less than the previous value, subtract it if ($currentValue < $prevValue) { $total -= $currentValue; } else { $total += $currentValue; } $prevValue = $currentValue; } return $total; } } $test = new Solution(); $result = $test->romanToInt("XXVII"); // Example usage

This code defines the `romanToInt`

function, which takes a Roman numeral string as input and converts it to an integer using the specified Roman numeral rules. It iterates through the string in reverse order and calculates the total integer value.

The line `$currentValue = $romanValues[$s[$i]];`

is responsible for obtaining the integer value associated with the current Roman numeral character in the string.

Here’s how it works:

`$s`

is the input Roman numeral string.`$i`

is the current index in the string, which is used to access the character at that position.

So, `$s[$i]`

retrieves the Roman numeral character at the current index.

For example, if you have the Roman numeral string “XXVII” and `$i`

is currently pointing to the last character ‘I’, then `$s[$i]`

would give you ‘I’.

`$romanValues`

is an associative array that maps Roman numeral characters to their corresponding integer values. For example, it has the mapping ‘I’ => 1, ‘V’ => 5, ‘X’ => 10, and so on.

So, when you write `$romanValues[$s[$i]]`

, it looks up the integer value associated with the Roman numeral character at the current index.

In summary, this line allows you to obtain the integer value of the current Roman numeral character in the input string, which is essential for the Roman numeral to integer conversion.

To access an element in the associative array `$romanValues`

, you use the key associated with the element inside square brackets. The key is the Roman numeral character, and the value is the corresponding integer.

Here’s how you can access elements in the `$romanValues`

array:

$romanValues = [ 'I' => 1, 'V' => 5, 'X' => 10, 'L' => 50, 'C' => 100, 'D' => 500, 'M' => 1000, ]; // Accessing elements $valueOfI = $romanValues['I']; // $valueOfI will be 1 $valueOfV = $romanValues['V']; // $valueOfV will be 5 $valueOfX = $romanValues['X']; // $valueOfX will be 10 // ... and so on

In the above code, we access the value associated with each Roman numeral character by specifying the key (Roman numeral character) inside square brackets after the array variable `$romanValues`

. This retrieves the corresponding integer value.

So, for example, `$romanValues['I']`

gives you the value 1, and `$romanValues['V']`

gives you the value 5. You can use this approach to access any element in the associative array based on its key.

The syntax `$romanValues[$s[$i]]`

involves nested indexing, where you’re accessing elements in an associative array using values obtained from another array.

Here’s a breakdown of how it works:

`$s`

is the input Roman numeral string.`$i`

is an index variable that represents the current position within the string.

Now, let’s break down the nested indexing:

`$s[$i]`

: This part retrieves the character at the current index`$i`

in the string`$s`

. For example, if`$i`

is currently pointing to the last character ‘I’, then`$s[$i]`

would give you ‘I’.`$romanValues`

: This is an associative array that maps Roman numeral characters to their corresponding integer values. For example, it contains mappings like ‘I’ => 1, ‘V’ => 5, ‘X’ => 10, and so on.`$s[$i]`

represents the Roman numeral character at the current index. For example, if`$i`

is pointing to ‘I’, then`$s[$i]`

is ‘I’.`$romanValues[$s[$i]]`

: This part of the line looks up the integer value associated with the Roman numeral character`$s[$i]`

in the`$romanValues`

array. In other words, it uses the character obtained from`$s[$i]`

as the key to access the corresponding numeric value in the array.

Putting it all together, `$romanValues[$s[$i]]`

allows you to access the integer value that corresponds to the Roman numeral character at the current index in the input string `$s`

. This is essential for converting Roman numerals to integers because it helps you look up the numeric values associated with each character in the Roman numeral string.